"Sign About" books by Anthony Lewis are available on Amazon.com & they're a nice, easy way to introduce signing to your baby. If you're interested in learning more about Language Development there'sgood info. on www.Talaris.org & also www.zerotothree.org.
Joseph Garcia developed the SIGN with your BABY program & his popular book is called Baby Signs. He also has a DVD, both are available through the King County Library System.