My fourteen-month old currently signs eat, more, Mommy, Daddy, dog, fish, flower, train, banana, ball, cheese, grapes, baby, milk, water, cookie, strawberry, apple, sleep, and cracker. I cannot say enough about how fantastic it is that she can walk up to me and tell me that she's hungry and exactly what she wants, instead of crying or fussing. The only negative I can think of is that I do have family that is convinced she'll never speak if she signs. To that I say, how many fourteen-month olds say Mama, Daddy, dog, fish, thank you, duck, uh oh, bye bye, no, kitty, flower, baba (for drink), ball, and more? The research shows that sign language builds vocabulary, and clearly that's true.
BTW, there are some videos on the web at www.signingtime.com that are fantastic. The videos focus on teaching words and signs and are extremely well done. We don't let our daughter watch them very often, but she really loves them. My husband and I have been using them to learn signs ourselves. They're cute with catchy music that doesn't cross over into annoying. That's important to us since I'm sure we'll be hearing/watching the vidoes over and over and over and over for the next few years!