So it's kind of old news now, but there were some differing opinions when WOTC announced the Monk playtest, and made it a psionic class. It doesn't bother me, though. Actually, I was thinking of assigning the monk to all the official power sources in order. Let's go:
Martial Monk - Easy. The 4E Monk already looks half martial, enhancing his martial skills with latent psionic powers.
Divine Monk - The word "Monk" certainly brings the divine power source to mind. The divine Monk is a warrior empowered by her god, much like the Avenger (PHB2).
Arcane Monk - Now it gets trickier. Still, a guy with no armor, no weapons and a decent special effects budget could certainly be magical. Hadoken!
Primal Monk - Okay, this is pretty far off. Still, the Barbarian's rages channel the aspects of certain animals to give him those aspects. The Monk could do the same and be a decent unarmored fighter (but far from the "ascetic on a mountain").
Psionic Monk - Official. As I said, I don't mind the idea. I figure it's very weak psionics, only enough to enhance personal training and sometimes flip out with some kind of blast.