Where to find the most common RDF/XML namespace prefixes/base URLs as a snippet?

I'm not aware of any lists as such but what you want is probably prefix.cc, it's a service created by Richard Cyganiak from DERI and it's basically a lookup service for prefixes. Enter a prefix and it'll give you one/more Namespace URIs typically associated with that prefix.

As far as I remember it also allows you to export prefixes in various formats such as RDF/XML snippets.

This is the set of namespaces that I use most often, which might be of use:

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" 
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
xmlns:owl="http://www.w3.org/2002/07/owl#" 
xmlns:dc="http://purl.org/dc/terms/"
xmlns:foaf="http://xmlns.com/foaf/0.1/" 
xmlns:vcard="http://www.w3.org/2006/vcard/ns#"
xmlns:dbp="http://dbpedia.org/dbprop/"
xmlns:geo="http://www.geonames.org/ontology#"
xmlns:gr="http://purl.org/goodrelations/v1#" 
xmlns:commerce="http://search.yahoo.com/searchmonkey/commerce/"
xmlns:media="http://search.yahoo.com/searchmonkey/media/" 
xmlns:cb="http://cb.semsol.org/ns#" >