Some MOBA are pretty good (if you can deal with all the angry players). I like Lol, DotA and Smite.

Renaissance Heroes is also a nice game.

Runes of magic or Dota 2

dota 2

LOL

None. I try avoid games with microtransactions.

Cry of Fear is currently my favorite.

Rusty Hearts.
Bit of an underdog, but it's a good brawler with surprisingly solid combo mechanics etc. and funny plot.
Cash shop does sell stat-boosting items, but I've not seen stuff that makes that game-breaking (At most around 5% stat increase and if you're good enough at the game you don't really need that).

Quake Live

Tales Of Maj'Eyal: Age Of Ascendancy aka TOME

link: http://te4.org/

Right now it's Phantasy Star Online 2.

TF2

TF2 and DwarfsF2P :)

Neverwinter

I don't play a lot F2P games at the moment, but I did play an awful lot of Tribes Ascend and Battlefield Heroes, and can't really decide between those two games.

Tribes: ascend

League Of Legends, Warframe

osu!

Tribes : Ascend for me.

My tastes changes over time, but I really enjoyed World of Tanks for a long long time and right now I'm really addicted to Warframe. For a free game is incredibly good and the devs really listen to the players' opinion (it's still in BETA phase).

drift city WAS a good game, but too few players were interested in it, and there were too many microtransactions.

I wish someone released something similar. It was graphically similar to borderlands, with a cartoony world for your cartoony (but stylish, pseudo realistic and definitely based ON real cars) cars to drive in.

Stronghold: Kingdoms

planetside 2

Dota 2.

Fortress of Hats 2 is pretty good, I guess.