Here's a great kit for starting sign with your babies: SIGN with your BABY - Baby Sign Language (ASL) Kit: Includes Book, How-to DVD, Quick Reference Guide
It includes an instructional DVD for parents, a book with sign dictionary, and a laminated quick-reference sign sheet (which is handy to share with sitters).
I also highly, highly recommend the Signing Time DVD series for toddlers and preschoolers. My kids love it! (My husband and I don't mind them either, although we think Rachel, the hostess/teacher, becomes more confidant and polished as the series goes on.)
There are two seasons with multiple volumes per each. There is a third series, Baby Signing Time, but I don't like showing babies a lot of DVDs and I like the toddler/preschool ones better. Here's season 1, volume 1 as well as a couple package options to get you started.