My son is now 15 but he has been there with the "I don't know", and I just wanted to put a little perspective on it. My son wanted to be surprised. He knew he was getting older and really "didn't believe" anymore, but just wasn't (and isn't ready) to give up the Christmas joy. It really is not the same when you know everything under the tree.
With that being said, I do the following:
I get him some clothes. I just ask the other kids in the store shopping. Most kids are cool with this. I know what stores my son considers cool, and I go there. I actually buy what is "cool", not just what is on the sales rack, it is Christmas afterall.
If he is a gamer and has and Ipod, accessories are your friend and probably not his. My son goes through headsets like they are water. I get him a few cheaper kinds and a good pair.
Real headsets. If he does online gaming a nice headset with a mic is invaluable.
Gift cards to movies, food places, and things like lasertron in your area. I get all the types of social places he will go. He feels like he is growing up using his own money and not always having to ask. Plus if there is no snow or grass to cut, he has some extra money.
If you know his gamer friends, ask what games they may be adding to the playing time.
A wallet - a real one. Trust me, this becomes an invaluable gift.
*for the gift cards, I usually buy a small gift like a rubics cube to wrap it up with, makes the gift cooler to unwrap.
Have a great Christmas!!!

