http://asl.ms/

http://www.handspeak.com

http://www.asluniversity.com/

http://commtechlab.msu.edu/sites/aslweb/browser.htm

I do NOT recommend aslpro.com, while it is a neat site there are some signs that are wrong, and if you don't know if the sign you're looking at is correct or wrong, it makes the site unuseable.