Just the cards, in calligraphy, with everything you feel about him beautifully scripted. You could put in reasons you love him, or write everything you feel for him. Even better, be witty in your writing, be creative, and steal his heart with your wits. You could find out funny birthday one liners, and put them on paper.
Select your favorite restaurant for the dinner party, take him there, and surprise! A karaoke night! Wait for your turn, and sing aloud his favorite song in front of everyone. Dedicate it to him, and capture that look on his face while he sees you making a complete idiot of yourself (oops, that might happen if you don't know how to sing). Something like Hilary Swank does in P.S. I Love You. Well, why not call him on the stage and sing along?
Not necessarily football, it could be any sport for that matter. You just need to take care of the next match of his liking, and book two tickets for that. So what if you abhor his favorite sport? Isn't it enough that you've decided to go to watch the match with him? Too much sentiments, eh? That's what he'd love the most about you.
What's your boyfriend's new age that he's going to flaunt all yearlong? Let's assume he turns 21 this birthday. All you've got to do is buy 21 inexpensive items, and put them all in a gift basket decorated by you. These items could range from a pen to a shower gel, an electric razor to a pair of socks... anything that might come handy to him! Well, this gift really depends upon how much you know him and his needs.