First off: guys are NOT hard to buy for. Here are a few things you can buy that he'd like:
tight, low-rise jeans
miniskirt (skin-tight black leather, preferably)
scandalously revealing bikini
bra
thigh-high stockings
panties (crotchless, to allow for easy access in crucial situations)
high heeled shoes
transparent teddy
pretty much anything from the Victoria's Secret catalog
--huno
P.S.: BTW, these aren't actually for him--they're for you... which is a great present for him.

And if none of this is what you're looking for (or you already have all this stuff), get him a nice pair of shoes. I always find myself wishing I had a nice pair of shoes because I quickly scuff up my best pair...