I have found this to be very different from kid to kid. My son, at 8 and 9, still loved toys (heck, he will be 12 this year and he likes collecting Halo figures, pokemon games, etc..) Some of his peers were "so over" toys and wanted sports memorabilia, sporting items (caps, phiten necklaces, etc...), and more "teen" type items than my DS was into. We like Legos here but I can't name many boys in DDs (3rd) grade who had them on their wishlist at Christmas.
What I have given for years was $10 in a card. That is what most people were giving and I got tired of trying to be original and "age appropriate"

DH and I joke that we are "loaning" so and so's parents $10 until our kids birthday because that's all we do is trade $10 around to the kids but.......they seem to like it. I know my DS would much rather get money he can stockpile towards something he wants than be given sports jerseys, hats, batting gloves, etc..
Another idea is iTunes cards if the child has an iPod. My oldest two really love getting on iTunes and buying with their "own" money (especially since I refuse to link a CC to iTunes LOL)