Here's an idea to redesign monk from the ground up. Let's review where they fit in:
Clerics/Druids/Favored Souls: powered by divine magic
Sorcerers/Wizards/Warmages: powered by arcane magic
Warlocks: powered by eldritch forces (I guess)
Bards: powered by some arcane magic, and some supernatural musicianship
Psions/Psychic Warriors: powered by the mind
Monks: powered by ki.

I think that ki powers would help solve both the problems the monk has (lack of contribution, lack of differentiation). Abundant step, quivering palm, and ethereal body are only 3 examples of ki powers that monks can attain. Ki powers would naturally use power points/day. So if we introduced a six level ki powers chart and perhaps 3 or 4 schools of powers, all the sudden monk is surprisingly similar to psychic warrior, a melee class with lots of variety and powers. Because monks have flurry, diamond body, and many other special qualities, and because I still want to have them gain kensai-like weapon enhancement ability, they wouldn't have as many power points as psychic warriors per day.