I've heard some pretty heavy hitters are jumping into web-based MMORPGs big time.

Expect to see some YC apps this fall based around games. Speaking of which, are there any YC game startups? (can't remember offhand)

Here's a French game that I think is ripe for duplication and scaling.

http://rms.miniville.fr/ You play by posting your link and your city gets bigger when other people visit it.