I just came across this online sign dictionary at
http://www.signwithme.com/002_browse_signs.asp
It has a verbal description of the sign, a video and suggestions at to when to use it. I found it very helpful. (I’m sorry if someone has already mentioned this site and this is just a repetition, but this forum is soooo huge by now to look through all the threads…)
Another really great online resource is Signing Savvy. It’s an online video dictionary with about any word you can think of! 