It depends on what you want out of a monk. Oriental Adventures has a couple of nice PrC (Tatoo monk specificiall), The WoTC diamond warrior PrC makes monk/psi-warrior a feasible option, and Hero's of High Favor: Half-Orcs has an awesome idea for a barb/mnk or mnk/barb.
Little suprised you didn't recommend Monk of the Sacred Chain Psion. Sure it's a Calastian Prestige class and therefore Chardunite/Scarred Lands stuff. But COME on! Monk of the Sacred Chain ROCKS!
It's one class in a setting specific supplement. If he wants to check it out, that's cool, but it seems like a lot of money to spend for one class if you aren't playing SL.