Anarchy Online has a free version of their online game. It's limited, there's a lot of fancy-schmancy new places you can't go, and stuff you can't use. But, it's pretty darn similar to the original version of the game (before the expansions). And, you know - free!

I don't play *all* the time, but sometimes when I need a break from reality, it's a really fun diversion for me.