I found an excellent browser based MMO called Fallen Sword-
I didn't think just HTML and PHP could pull off a game that is very fun but they have done it. Best of all it is expansive, offers many features, and is free. Plus it is easy to jump in and jump out of the game, making it a great game for more casual players like myself.
Check out http://www.huntedcow.com/ , they make quiet a few BB games, all of them look pretty good.