UT, Quake Live is fun, it was F2P now you have to pay for it, but its on Steam, so meh.
Tribes. I LOVED that game, i was in the Alpha and paid for Premium, now everything is free, so I'm peeved. They dropped a huge patch a few months ago after they completely dropped the game in support of Smite. Tribes is now an amazing game, but its too late. It has a really high skill ceiling so could be great for 1v1