ASL Pro
This site offers a free comprehensive ASL video dictionary.

ASL University
This site is a great resource that includes an expansive ASL dictionary, free online lessons, and information on Deaf culture.

Baby Hands Productions
Although this website sells baby sign-language products, it also offers a number of free resources including a video dictionary and tips on signing with your baby.

Sign Language Videos on About.com
Just do some quick searching to find a variety of instructional videos on topics like how to sign the alphabet in ASL and common baby signs.

Signing with Your Baby
This is an informative website written and maintained by a signing mother.

Using Sign Language with Your Baby
A basic overview of how to start teaching signs to your baby, plus additional resources on deaf culture.