I got out my book from a child development class to see about this. My book says that at around 12 months it is normal for an infant to say their first recognizable word. They also say the temperament plays a big role in when a child will begin to talk but they also say that when language is greatly delayed parents should consult someone. They don't say what "greatly delayed" is though. The book is good and you could get it from the library, Infants and Children by Burke
I think that if your child is communicating in ways other than words you could give it a few more months but if there is a real lack of communication or if you get the feeling that there is something wrong than you should do some further research and possibly talk to an expert.
Troll? Here's me...