United Nations stats (lots of goodies)

http://unstats.un.org

some free, some paid

http://infochimps.com/

AIS Data (Marine Traffic)

http://www.aishub.net/

http://www.marinetraffic.com/ais/

And there's a great list of sources on Quora

http://www.quora.com/Where-can-I-get-large-datasets-open-to-...