Chainmail Bikini Games has a very short book called Beyond Monks - that has a Martial Artist Class, which is passable (although built for 3rd edition rules, if that bothers you).
Making a "Martial Artist" core class is filled with design problems:
1> Fighters Suck. The jury is out on whether the single classed Fighter is the weakest viable build or one of the strongest non-viable builds, but the fact remains that the SC Fighter sucks. Alot. That means that any time you make a class which essentially just beats people up in combat you are forced to either invalidate a previously existing core class or make a class that itself sucks. Not a pleasant prospect - especially when you are doing something whose concept doesn't lend itself to multiclassing terribly well.
2> D&D "game balance" is predicated on equipment. This is a much more subtle point, but it keeps coming back to kick people. You see, Paladins and Barbarians are supposedly balanced against Wizards, Clerics, and Druids based on the concept that they have equipment. Magic Swords, Magic Pants, the whole thing. If characters don't have this sort of equipment, the warriors can pretty much go home while the druid doesn't even really notice. So a "martial artist" has to be balanced against a "knight" when the knight has a magic sword. Because if the game is balanced right now - the knight does have a magic sword.
So it's another damned if you do, damned if you don't design problem. If you write your Martial Artist so that he is actually balanced against a knight in shining armor with a magic sword - the class is unbalanced as he's just like the knight except he doesn't need the magic sword. But if you design the Martial Artist so that he is in any meaningful way weaker than the knight in shining armor with the magic sword - you've created a class which is ass, as in reality the knight in fact does have that sword.
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Given those fundamental design problems - it is unsurprising that I've never been fully happy with any of the "martial artist" class concepts presented in any WotC or 3rd party supplement. It's simply not possible to build such a class which is balanced in light of the fundamental design mistakes made in the already existant warrior classes. Without overhauling the Fighter, you can't make a satisfying Martial Artist.
-Frank