Alien Swarm on steam - free alienbreed-esque shorter.
Left for Dead 1 and 2 are also goodies to have if you can get them in sales. We do play a few games of those from time to time - well those of us who use steam and own them.
In fact steam in general - just be prepared to never have any money ever as it sales are great and even out of sale deals can work well.
Lotro goes F2P on Sept 10th. Have you played it before (paid or trials?). Im getting back into it more lately. F2P may find it busier and so on, either way im enjoying it again.
EVE is what you make of it, or you have to be a masochist
(Im probably one).
WAR has a freebie mode - max level is 10 on their freebie. Kurttie is active there and I log various accounts, paid/free, every so often.