Vortex Wars

EFFACÉ

Portal 2?

it's not very online

Not sure if you are looking for something long-term, but if you like simcity, you might want to check out settlers online or anno online (just got to open beta)

EFFACÉ

Check out this game. http://www.chivalrythegame.com/blog/ It's not free though, unfortunately. ($25)

You might like Zatikon. It's like chess but with a lot more pieces and there's PvP, PvAI and P+PvAI

There is the option to spend $20 and you get different units but the pay-for units aren't better, they're just different and give you more scope for creating your own strategy. Most people I've played against haven't paid for the extra units.

http://www.chroniclogic.com/zatikon.htm

Plasma Burst 2. Free, 42 levels with loads of custom maps, and multiplayer mode. As well as a few VWers.
I don't have many more however.

I've not played it but this game looks pretty good

http://atwar-game.com/home/

Day/War Z. Both zombie games. The only noticeable difference is the first word of each title.

Hey ozserf, you could try wheel shock live 2. It's a fun multiplayer game also.