money, the amount depends on how well you know him
Buy him a Ferrari.
Depends what his interests are and your budget but I think you can't really go wrong with: money, giftcard from decathlon/mediamarkt/dreamland, itunes card. You could also pay for a fun day out: movie tickets, walibi/aqualibi/oceade tickets, karting session, game of bowling, etc. Other possibilities for this age which are less impersonal: a "cool" set of headphones, skateboard/longboard, portable pingpong set from decathlon, bow & arrow set from decathlon, sportscamera, elaborate lego set, ipod touch, etc. Hope this inspire you a bit! I personally don't like giving money but it's true that many kids that age like receiving it (but not all, my boys prefer more personal presents, especially "experiences"/fun days out which they wouldn't really think of themselves).
An anniversary party with his friends at Atelier Lollipop www.atelierlollipop.be
He can choose the theme he likes the most.