So he's got an iPod. Can we assume that it is the regular full-sized version, as you didn't append a shuffle, mini, or nano to the end?
Does he use it a lot, or does he sometimes not take it for running or working out? In other words, does he need a shuffle or nano, too?
Good earphones? Shure makes some great products.
Speaker/dock set-up? JBL OnStage, Altec InMotion, Bose SoundDock are all nice accoutrements for an iPod.
Is he a gamer? A Sony PSP or Nintendo DS is a darn nice stocking stuffer.
Does it even have to be a tech-y gift?