Other programming contest sites are good sources of problems similar to the ones that come up in interviews.

http://train.usaco.org/usacogate

http://community.topcoder.com/tc

http://uva.onlinejudge.org/

http://www.facebook.com/hackercup

http://code.google.com/codejam/

http://codeforces.com/

http://www.interviewstreet.com/recruit/challenges/