Hmmmm.. I am thinking.. I know there are a ton of older ones that my kids used to play when they had theirs.. might be able to get them at a used game store.. there was All the different Mario games.. they loved them...Lego has a lot for the boys (I think you have a boy right?) and those my son got a lot of fun out of. My youngest girl loved the kim possible game and lizzie mcguire. And suite life is another one they like a lot...
Here is a page that I just found that has a lot of the games they have always played and love.. might help you some
http://www.shopping.com/xPP-Game_Boy_Advance_Games~PG-2