Grunts by Mary Gentle. Orcs get into a stash of modern weaponry...the kind of cursed (or blessed) weapons that change people's personalities...leading the Orcs to become Orcish marines of a sort. Funny.
Brooks has a few more of the Magic Kingdom books you might read...they're all of the same light-hearted sort of fantasy.
David Edding's Belgariad (and Mallorean) can be downright funny.