♪♫ Anything Monks can do Rogues can do better /
Rogues can do anything better than you ♫♪

What's the purpose of a D&D monk? All fluff aside he's a hit-and-run light skirmisher. The Rogue does that job better, with added trap-finding and 'public face of the party' goodness.

The monk is fun and flavourful; but even with fun prestige classes like Drunken Master, Tattooed Monk or Fist of Zuiken it's no power player's option.