Hi Nicola, although there isn't mcuh to worry about just yet, there are a few things that you can do to help him along.
Such as if he asks for something by grunting or babytalk, that would not be easily understood by an outsider (if he doesn't use the actual word, or attempt it) then don't give it to him until he uses the word, or attempts it at least. I know this would be very hard, but it does work, and I've seen a few sucesses with it personally.
Another activity you could try is a naming game, where you can get flashcards at a the cheapie store, and they usually have animal, item, car, house pictures on them, and show them to him and point to the pic and say 'look, this is a cat, can you say cat? What sound does a cat make? Can you purr/meow like a cat?' Then just give alot of praise for any attempt he makes.
I personally think that if he is up and running about, has good balance, good tactile skills when handling objects and can manage intricate puzzles (for his age) then I wouldn't worry too much. Indeed if he gets to 3yrs old and is still not communicating very much and you are concerned, then definitely consult your doctor.
From the sounds of it he can understand you well and is just taking his time with words, and may well shock you when he does start talking at how well he can pronounce his words. You may find that he is taking in new words all the time, and is quietly building up hos vocabulary library, and will suddenly start yakking away as well asif not better than others his age.
All the best to you, sorry for the big long ramble, but felt I needed to get it all said. Do keep us in the loop with how he is doing. I think you will find that once he finally starts talking you will want him to just be quiet for two minutes! Enjoy it while it lasts.