I was given one of those radio controlled helicopters for my birthday. It is brilliant. Appeal to the kid that is still inside him and he will think you are so perceptive and that you really understand him!
PS, don't get him a gift card unless you don't really like him very much. He won't thank you for it.
Gift card to some store he likes.
a giftcard to his fave place/store etc...
a shirt of his fave band/show etc...
answer mine: http://ca.answers.yahoo.com/question/ind…
CD's you know he hasnt got for bands you both like so you can listen to them together
Beer...but seriously, if you have ever heard him mention something he likes or would like to do, that would be the best thing to give him. (within financial means...not like a corvette or something) Best of luck.