Well, my step-dad enjoys a big can of beer. So I got him a card, a Budwieser glass, and a big can of beer.
write him a something. . . hand write it. Itll show that you actually put some time and effort into it.
Might be too late, or not, to do this, but try spending the day with the guy on you. Go to a movie (The Fast and the Furious: Tokyo Drift is out and if he likes cars, bingo), play a session of golf at the driving range, go for a drive in the country, go bowling or play some billiards, etc.
you should just be like me, and not him anythign at all! he had to remind me like 4 times it was fathers day