Event tickets are a great gift for a boyfriend. I buy 2 or 4 tickets for the same event. Baseball, football, car show and concert tickets are all good options.
I believe in a personal, yet unexpensive gift for a boyfriend. I would suggest a watch, underwear, or cologne. I would not buy a boyfriend gift cards or certificates, household items, or cash. It is too thoughtless and unpersonal. Also, guys are not picky about gifts like women, so you have a good chance of buying the perfect gift!
I suggest paying attention to your boyfriend all the time and picking up clues. If he says he wants or needs something put it in the back of your head and when its time to get gifts you will have something meaningful. This will make him happy you were thoughtful.
Tickets to his favorite sporting event, satellite radio for his car, tools... but make sure he doesn't have them already, or need other things to use them with.
The best gifts are the most personal. Obviously, if he has any hobbies, gifts relating to them are a good idea. Even better, though, are gifts that you can share together like tickets for both of you to see his favorite team, or a gift card for his favorite restaurant.