Your his girlfriend, you should know what he likes or dislikes. Some of us guys are much more simpler. When I say I don't want anything for birthday it often means that, outside of the fact that I will accept spending the day with girlfriend on couch eating pizza and watching tv or alternatively I will also accept birthday sex. Unfortunately I ain't got a girlfriend so my birthdays are often spend by myself watching tv and dreading to have lived yet another year.
I would get him a sexy watch. Guys love to wear watches. Or get him some gym membership card or something if he likes Woking out. Get him a gift card for some men clothing store. Don't get him clothes on your own you can never know what guys like.