GURPS: Martial Arts, co-authored by Peter D of Dungeon Fantastic. It is no longer in print so I have been following the prices of used copies on Amazon. They have been hovering north of $50 for quite a while but some careless bookseller listed it for $22.77 and I pounced (the next cheapest copy was over twice that price). The book arrived yesterday and is in great condition.
GURPS books are always well-researched and well-written. GURPS: Martial Arts is no exception. It covers much more than the usual Eastern unarmed combat, although there is plenty of that sort of thing. Lots of options for melee weapons, too. And I now understand why I was often confused by GURPS...our Majestic Wilderlands group is using a lot of the MA options. Rob did create a handy cheat sheet, which helped a great deal. But now I can read the source as I hold it in my hands (not a fan of reading things like this as a PDF).
My only complaint is the illustration of the blow to the groin. Unlike most art, it doesn't get me psyched for gaming.