When I was little, I was actually fluent in sign language so I was lucky and didn't have to look up the words. But this is the best website (in my opinion) to learn the words. It includes a video to show you how to sign each word. http://commtechlab.msu.edu/sites/aslweb/browser.htm
Another website is called "Signing with your Baby" and it has books, DVD's, and flash cards that you can buy in addition to online pictures of common words to teach your child.
On a side note, although I taught "A" the correct signs, he chose to change some of them. For example, he refuses to sign "done" the way I showed him. Instead, he throws up his hands when he's done. I didn't fight him with it, and now we both know when he's done.
Good luck and happy communication!!! :)