http://ebiquity.umbc.edu/resource/html/id/196/Most-common-RDF-namespaces gives
a list of 284 of the most common namespace URIs in their data set
("data collected from swoogle on 22 August 2006").

For each URI, anything after (and including) a '#' character was stripped, and
the resulting URI was downloaded with curl on 2009-05-15.

The counts of each HTTP response are:

     14 HTTP/1.0 200 OK
      1 HTTP/1.0 301 Moved Permanently
      2 HTTP/1.0 302 Moved Temporarily
      2 HTTP/1.0 404 Not Found
    122 HTTP/1.1 200 OK
     23 HTTP/1.1 301 Moved Permanently
     38 HTTP/1.1 302 Found
      1 HTTP/1.1 302 Moved Temporarily
      1 HTTP/1.1 303 See Other
      2 HTTP/1.1 403 Forbidden
     54 HTTP/1.1 404 Not Found
      2 HTTP/1.1 502 Bad Gateway
     22 not responding

The list of URIs grouped by HTTP response:

HTTP/1.0 200 OK
  http://bitzi.com/xmlns/2002/01/bz-core#
  http://person.org/BusinessCard/
  http://rssnamespace.org/feedburner/ext/1.0
  http://semspace.mindswap.org/2004/ontologies/Crew-ont.owl#
  http://semspace.mindswap.org/2004/ontologies/ShuttleMission-ont.owl#
  http://trust.mindswap.org/ont/trust.owl#
  http://www.mindswap.org/2003/owl/mindswap#
  http://www.mindswap.org/2003/owl/project#
  http://www.mindswap.org/2003/owl/swint/person#
  http://www.mindswap.org/2003/owl/swint/terrorism#
  http://www.mindswap.org/2004/owl/mindswappers#
  http://www.mindswap.org/2004/owl/mindswap-projects#
  http://www.mindswap.org/2004/www04photo.owl#
  http://www.mindswap.org/~glapizco/technical.owl#

HTTP/1.0 301 Moved Permanently
  http://en.wikipedia.org/wiki/

HTTP/1.0 302 Moved Temporarily
  http://mindswap.org/2005/owl/photomesa#
  http://owl.mindswap.org/2003/ont/owlweb.rdf#

HTTP/1.0 404 Not Found
  http://www.mindswap.org/~golbeck/web/www04photo.owl#
  http://www.sixapart.com/ns/at

HTTP/1.1 200 OK
  http://ajft.org/foaf.rdf#
  http://backend.userland.com/blogChannelModule
  http://chefmoz.org/rdf/elements/1.0/
  http://dublincore.org/2000/03/13/dcq#
  http://dublincore.org/2000/03/13/eor#
  http://dublincore.org/2003/12/08/dctype#
  http://ebiquity.umbc.edu/ontology/assertion.owl#
  http://ebiquity.umbc.edu/ontology/association.owl#
  http://ebiquity.umbc.edu/ontology/contact.owl#
  http://ebiquity.umbc.edu/ontology/event.owl#
  http://ebiquity.umbc.edu/ontology/person.owl#
  http://ebiquity.umbc.edu/ontology/project.owl#
  http://ebiquity.umbc.edu/ontology/publication.owl#
  http://ebiquity.umbc.edu/ontology/research.owl#
  http://eulersharp.sourceforge.net/2003/03swap/log-rules#
  http://eulersharp.sourceforge.net/2003/03swap/rdfs-rules#
  http://eulersharp.sourceforge.net/2003/03swap/xsd-rules#
  http://example.org/
  http://gmpg.org/xfn/1#
  http://impressive.net/people/gerald/2001/captivate-ns#
  http://impressive.net/people/gerald/2001/exif#
  http://inferenceweb.stanford.edu/2004/03/iw.owl#
  http://inferenceweb.stanford.edu/2004/07/iw.owl#
  http://madskills.com/public/xml/rss/module/trackback/
  http://morpheus.cs.umbc.edu/aks1/ontosem.owl#
  http://norman.walsh.name/knows/taxonomy#
  http://nulllogicone.net/schema.rdfs#
  http://nwalsh.com/rdf/
  http://nwalsh.com/rdf/cvs#
  http://nwalsh.com/rdf/exif#
  http://nwalsh.com/rdf/exif-gps#
  http://nwalsh.com/rdf/exif-intrinsic#
  http://nwalsh.com/rdf/exif-nikon5700#
  http://nwalsh.com/rdf/exif-nikon950#
  http://nwalsh.com/rdf/jpegrdf#
  http://prismstandard.org/namespaces/1.2/basic/
  http://protege.stanford.edu/plugins/owl/protege#
  http://protege.stanford.edu/system#
  http://rdfs.org/sioc/ns#
  http://redfoot.net/2002/10/red#
  http://redfoot.net/2005/template#
  http://russell.rucus.net/2004/clique/#
  http://simile.mit.edu/2005/04/flair#
  http://snipsnap.org/rdf/snip-schema#
  http://storymill.com/mu/2005/03/
  http://usefulinc.com/ns/doap#
  http://veggente.berlios.de/ns/RIM_CMET#
  http://veggente.berlios.de/ns/RIMDatatype#
  http://webns.net/mvcb/
  http://web.resource.org/cc/
  http://web.resource.org/cc/#
  http://www.aktors.org/ontology/portal#
  http://www.aktors.org/ontology/support#
  http://www.confoto.org/ns/confoto#
  http://www.daml.org/2000/10/daml-ont#
  http://www.daml.org/2001/03/daml+oil#
  http://www.daml.org/2001/10/html/airport-ont#
  http://www.daml.org/2002/02/telephone/1/areacodes-ont#
  http://www.daml.org/services/owl-s/1.0/Process.owl#
  http://www.daml.org/services/owl-s/1.0/Profile.owl#
  http://www.daml.org/services/owl-s/1.0/Service.owl#
  http://www.daml.org/services/owl-s/1.1/Process.owl#
  http://www.example.org/
  http://www.hackcraft.net/bookrdf/vocab/0_1/
  http://www.isi.edu/webscripter/bibtex.o.daml#
  http://www.iwi-iuk.org/material/RDF/1.1/descriptor/#
  http://www.iwi-iuk.org/material/RDF/1.1/Schema/Class/mn#
  http://www.iwi-iuk.org/material/RDF/1.1/Schema/Property/mnp#
  http://www.iwi-iuk.org/material/RDF/Schema/Class/iwi#
  http://www.iwi-iuk.org/material/RDF/Schema/Descriptor/midesc#
  http://www.iwi-iuk.org/material/RDF/Schema/Property/iwip#
  http://www.kanzaki.com/ns/exif#
  http://www.ksl.stanford.edu/software/IW/spec/iw.daml#
  http://www.loc.gov/marc/relators/
  http://www.math.org/#
  http://www.openmobilealliance.org/tech/profiles/MMS/ccppschema-20050301-MMS1.2#
  http://www.openmobilealliance.org/tech/profiles/UAPROF/ccppschema-20021212#
  http://www.ukoln.ac.uk/metadata/rslp/1.0/
  http://www.usemod.com/cgi-bin/mb.pl?ModWiki
  http://www.w3.org/1999/02/22-rdf-syntax-ns#
  http://www.w3.org/1999/xlink
  http://www.w3.org/1999/xx/http#
  http://www.w3.org/2000/01/rdf-schema#
  http://www.w3.org/2000/07/04-ccpp#
  http://www.w3.org/2000/07/uri43/uri.xsl?template=
  http://www.w3.org/2000/10/annotation-ns#
  http://www.w3.org/2000/10/rdf-tests/rdfcore/testSchema#
  http://www.w3.org/2000/10/swap/log#
  http://www.w3.org/2000/10/swap/math#
  http://www.w3.org/2000/10/swap/pim/contact#
  http://www.w3.org/2000/10/swap/pim/doc#
  http://www.w3.org/2000/10/swap/pim/exif#
  http://www.w3.org/2000/10/swap/pim/travelTerms#
  http://www.w3.org/2000/10/swap/string#
  http://www.w3.org/2000/10/XMLSchema#
  http://www.w3.org/2000/PhotoRDF/dc-1-0#
  http://www.w3.org/2000/PhotoRDF/technical-1-0#
  http://www.w3.org/2001/02pd/gv#
  http://www.w3.org/2001/02pd/rec54#
  http://www.w3.org/2001/03swell/rcs#
  http://www.w3.org/2001/04/roadmap/org#
  http://www.w3.org/2001/10/daml+oil#
  http://www.w3.org/2001/svgRdf/axsvg-schema.rdf#
  http://www.w3.org/2001/sw/DataAccess/tests/result-set#
  http://www.w3.org/2001/vcard-rdf/3.0#
  http://www.w3.org/2001/XMLSchema
  http://www.w3.org/2001/XMLSchema#
  http://www.w3.org/2002/03owlt/testOntology#
  http://www.w3.org/2002/05/matrix/vocab#
  http://www.w3.org/2002/07/owl#
  http://www.w3.org/2002/11/08-ccpp-schema#
  http://www.w3.org/2002/12/cal/#
  http://www.w3.org/2002/12/cal/ical#
  http://www.w3.org/2003/01/geo/wgs84_pos#
  http://www.w3.org/2003/06/sw-vocab-status/ns#
  http://www.w3.org/2003/11/swrl#
  http://www.w3.org/2003/12/exif/ns#
  http://www.w3.org/XML/1998/namespace
  http://www.wapforum.org/profiles/MMS/ccppschema-20010111#
  http://xmlns.com/foaf/0.1/
  http://xmlns.com/foaf/0.1/#
  http://xmlns.com/wot/0.1/

HTTP/1.1 301 Moved Permanently
  http://amk.ca/xml/review/1.0#
  http://backend.userland.com/RSS2#
  http://bbc.co.uk/ns#
  http://downlode.org/rdf/os/0.1/
  http://kaywa.com/rss/modules/moblog/
  http://norman.walsh.name/knows/what#
  http://norman.walsh.name/knows/where#
  http://norman.walsh.name/knows/who#
  http://ns.adobe.com/iX/1.0/
  http://reports.eea.eu.int/EEAIndexTerms/ThesaurusSchema.rdf#
  http://swrc.ontoware.org/ontology#
  http://swrc.ontoware.org/ontology/ontoware#
  http://themes.eea.eu.int/ns/1.0/
  http://wellformedweb.org/CommentAPI/
  http://www.inrialpes.fr/opera/people/Tayeb.Lemlouma/NegotiationSchema/ClientProfileSchema-03012002#
  http://www.loc.gov/loc.terms/relators/
  http://www.nlm.nih.gov/mesh/2004#
  http://www.swi.psy.uva.nl/mia/vra#
  http://www.w3c.org/1999/02/22-rdf-syntax-ns#
  http://www.w3.org/1999/xhtml
  http://www.w3.org/2004/02/skos/extensions#
  http://www.w3.org/TR/1999/PR-rdf-schema-19990303#
  http://www.w3.org/TR/WD-rdf-schema#

HTTP/1.1 302 Found
  http://hackdiary.com/ns/gps#
  http://home.netscape.com/NC-rdf#
  http://musicbrainz.org/mm/mm-2.1#
  http://purl.oclc.org/net/rss_2.0/enc#
  http://purl.org/dc/dcmitype/
  http://purl.org/dc/elements/1.0/
  http://purl.org/dc/elements/1.1/
  http://purl.org/dc/elements/1.1/#
  http://purl.org/dc/elemwnts/1.1/
  http://purl.org/dc/qualifiers/1.0/
  http://purl.org/dc/terms/
  http://purl.org/net/inkel/rdf/schemas/lang/1.1#
  http://purl.org/net/vocab/2003/11/photo#
  http://purl.org/net/vocab/2004/11/sparqling#
  http://purl.org/rss/1.0/
  http://purl.org/rss/1.0/modules/aggregation/
  http://purl.org/rss/1.0/modules/annotate/
  http://purl.org/rss/1.0/modules/company/
  http://purl.org/rss/1.0/modules/content/
  http://purl.org/rss/1.0/modules/event/
  http://purl.org/rss/1.0/modules/link/
  http://purl.org/rss/1.0/modules/reference/
  http://purl.org/rss/1.0/modules/slash/
  http://purl.org/rss/1.0/modules/syndication/
  http://purl.org/rss/1.0/modules/taxonomy/
  http://purl.org/rss/1.0/modules/textinput/
  http://purl.org/rss/1.0/modules/wiki/
  http://purl.org/vocab/bio/
  http://purl.org/vocab/bio/0.1/
  http://purl.org/vocab/relationship/
  http://purl.org/vocab/vann/
  http://smw.ontoware.org/2005/smw#
  http://www.cogsci.princeton.edu/~wn/concept#
  http://www.cogsci.princeton.edu/~wn/schema/
  http://www.purl.org/stuff/rev#
  http://www.schemaweb.info/schemas/meta/rdf/
  http://wymiwyg.org/ontologies/language-selection#
  http://wymiwyg.org/ontologies/transaction#

HTTP/1.1 302 Moved Temporarily
  http://rdflib.net/2002/InformationStore#

HTTP/1.1 303 See Other
  http://www.w3.org/2004/02/skos/core#

HTTP/1.1 403 Forbidden
  http://random.ioctl.org/#
  http://www.w3.org/1999/xlink/

HTTP/1.1 404 Not Found
  http://animaldiversity.ummz.umich.edu/local/keywords/keywords.owl#
  http://dublincore.org/2000/03/13-dctype
  http://example.com/app#
  http://example.org/stuff/1.0/
  http://fotonotes.net/rdf/fotonotes-schema#
  http://frot.org/space/0.1/
  http://gump.apache.org/schemas/main/1.0/
  http://igargoyle.com/rss/1.0/modules/img/
  http://img.cs.man.ac.uk/oil/oiled#
  http://jena.hpl.hp.com/2003/03/result-set#
  http://jena.hpl.hp.com/2003/08/jms#
  http://jena.hpl.hp.com/ENT/1.0/#
  http://jena.hpl.hp.com/semblog#
  http://lojjic.net/ns/rdf/blog/
  http://lojjic.net/ns/rdf/comments/
  http://lojjic.net/ns/rdf/photos/
  http://musicbrainz.org/mm/mm-2.0#
  http://norman.walsh.name/rdf/gallery#
  http://nwalsh.com/rdf/exif-canon#
  http://opencyc.sourceforge.net/daml/cyc.daml#
  http://projects.semwebcentral.org/owl-gforge/gforge-ont.owl#
  http://purl.org/rss/modules/syndication/
  http://purl.org/urfm/
  http://rdf.desire.org/vocab/recommend.rdf#
  http://redfoot.net/2002/12/23/log#
  http://semwebcentral.org/owl-gforge/site#
  http://spire.umbc.edu/ontologies/ethan_keywords.owl#
  http://spire.umbc.edu/ontologies/ethan.owl#
  http://spire.umbc.edu/ontologies/nhet.owl#
  http://swc.projects.semwebcentral.org/owl/gforge-ont#
  http://usefulinc.com/ns/doap/#
  http://wiki.livedoor.com/-/spec/1.0/
  http://www.aktors.org/ontology/base#
  http://www.aktors.org/ontology/signage#
  http://www.ecademy.com/namespace/
  http://www.example.com/schema#
  http://www.georss.org/georss/
  http://www.imc.org/vcard/3.0/
  http://www.megginson.com/exp/ns/airports#
  http://www.mozilla.org/rdf/chrome#
  http://www.mutopiaproject.org/piece-data/0.1/
  http://www.nature.com/schema/2004/05/news#
  http://www.nines.org/schema#
  http://www.rossettiarchive.org/schema#
  http://www.semblog.org/ns/semblog/0.1/
  http://www.w3.org/199/02/22-rdf-syntax-ns#
  http://www.w3.org/2000/01-rdf-schema#
  http://www.w3.org/2000/10/swap/pim/file#
  http://www.w3.org/2003/12/exif/ns/
  http://www.w3.org/2004/02/image-regions#
  http://www.w3.org/2004/ql#
  http://www.w3.org/vcard-rdf/3.0#
  http://www.wapforum.org/profiles/UAPROF/ccppschema-20010430#
  http://xmlns.com/wordnet/1.6/

HTTP/1.1 502 Bad Gateway
  http://usefulinc.com/rss/manifest/
  http://www.usefulinc.com/picdiary/

not responding
  http://bulkfeeds.net/xmlns#
  http://http://purl.org/dc/elements/1.1/
  http://jibbering.com/2002/3/svg/#
  http://jibbering.com/2002/6/terms#
  http://jibbering.com/vocabs/image/#
  http://medea.mpiwg-berlin.mpg.de/ure/vocab#
  http://medea.mpiwg-berlin.mpg.de/vlma/vocab#
  http://mutemap.openmute.org/2003/mcc#
  http://oiled.man.example.net/test#
  http://rdf.insee.fr/geo/
  http://semweb.mcdonaldbradley.com/OWL/TaxonomyMapping/Definitions/TaxonomySupport.owl#
  http://sophia.inria.fr/~enerbonn/rdfpiclang#
  http://visus.mit.edu/fontomri/0.01/units.owl#
  http://wiki.ontoworld.org/index.php/
  http://wiki.ontoworld.org/index.php/_
  http://wiki.ontoworld.org/index.php/_Attribute-3A
  http://wiki.ontoworld.org/index.php/_Relation-3A
  http://www.limber.rl.ac.uk/External/thesaurus-iso.rdf#
  http://www.softwarestudio.org/libical/UsingLibical/node49.html#
  http://www.trustix.net/schema/rdf/spi-0.0.1#
  java:java.util.Date
  urn:hl7-org:v3/mif