Are there any activities in the area that he enjoys that you could get him passes for, maybe a couple different activities? My DS would like gift cards for paintball, indoor skydiving, a sporting event, movie tickets, ice or roller skating, ziplining, things like that.
Don't forget fast food gift cards, gamestop, and of course, cash.
ETA: My DS is turning 14 next week and I have gotten to the point where he knows my budget for gifts and makes me a wishlist. It's not as fun, but at least that way I get what he wants. I will throw in a couple suprises, too, he knows he won't necessarily get everything on the list, but it gives me an idea of what he's thinking about. It's especially helpful because he has a tendancy to save up his allowance/mowing money and buy what he wants (which is great, but makes shopping for him harder) so that way I don't buy something he's planning on getting himself.