Lucy, that's so great you got him signing so early. My LO didn't actually sign back until maybe 13-14 months but when he did man was it useful!
... but what are some of the signs that you guys have found useful with babies? I was thinking more, finished, help, drink, eat, sleep, milk, mum, dad, time (as in time for food) and maybe some kids songs with animals and colours in them... Any other suggestions?
Bath, milk, more, again, sleep, crackers, blueberries, raisins, juice, water were the most useful signs around here. I basically stuck to things I knew he would want to ask for. Sleep sign was invaluable - he would do it to let us know he was tired. All the food and drink signs were all his favourites that he would want all the time, but along with that there were words he just said instead of signed at 14 months like "apple", "nanana" for banana, "orange", "rice".
No more signs now; the last one (milk) was dropped a couple of weeks back. We have 5 word sentence structures from him so I guess he didn't feel the need to sign to us any longer

- but still, it was great while it lasted.