My first answer to anything like this is always Titan Quest. It's my favorite hack and slash ARPG for when I just need things to die when I click the mouse a lot and want lots of shiny new things. The bundle with the expansion goes on sale on Steam for $5 fairly regularly, and the community is still active and has released and maintained a fanpatch [http://www.titanquest.net/tq-forum/threads/29712-REL-Bugfix-patch-1.17] to fix the remaining issues in the game. It's still the game on Steam I have with the most played hours after all this time. Every time I think I'm bored of it I convince someone else I know to buy it and play through it again with them and sink another 50-100 hours into it.
In other news, Dungeon Siege 3 is $5 today on Amazon [http://www.amazon.com/gp/product/B0054SFKUS/], which might be cheap enough to be worth it. I haven't tried it yet, and the reviews have been mixed, but enough people I know have said that it's enough fun to be worth it at that price that I grabbed a copy.
Edit: And I suppose A Valley Without Wind [http://www.arcengames.com/w/index.php/games/avww-features] would technically qualify. It's still in public beta, and not everything is finished yet, but what I've tried out so far has been interesting.