Some Datasets Available on the Web
datawrangling.com
datawrangling.com
I'm going to toss the ball into infochimps court for any deeper organization of the data, since they are already set up to handle it.
http://theinfo.org/
http://infochimps.org/datasets
http://ckan.org [Comprehensive Knowledge Archive Network]
http://www.trustlet.org/wiki/Repositories_of_datasets
http://www.daniel-lemire.com/blog/data-for-data-mining/
http://www.quantlet.org/mdbase/
http://datamob.org/
http://freebase.com/
http://infochimp.info/ics/data/ripd/www-personal.umich.edu/~mejn/netdata/
http://infochimp.info/ics/data/fixd/
http://infochimp.info/ics/data/pkgd/
http://infochimp.info/ics/data/rawd/
http://www.archive-it.org/public/all_collections