dota 2

Star Trek Online :-). I also played some Battlefield P4F and BSG Online. Also SWTOR, although their F2P system isn't very good.

What? Is War Thunder not gonna get any love?

Combat Arms used to be a pretty high on my list a few years ago. (Have mercy on me.)
Now, it's probably Smite or Blacklight: Retribution.

Currently I play only Path of Exile, but I've been thinking of trying Planetside 2.

Marvel Avengers Alliance

it's ok for a facebook game and honestly i haven't played a lot of the games I think i would like better like LoL, DOTA2, TF2, RoaMG, etc.

Dota 2

planetside2

League of Legends ^__^

Planetside 2, loadout seems like it might be a good F2P too

Neverwinter is kind of rocking my socks right now. I know f2p mmos are typically terrible, but this one might be a keeper.

Candy box

TF2 or Dota 2 (if that counts as F2P)

tf2

TF2,
was better when it was paid but still a good game

Dota 2 :)

A free game here, but just for real hipsters :P

TF2 <3

War Thunder I love that game!

Right now I'm alternating between Vindictus and Ragnarok Online 2. Vindictus is great for hack and slash, and RO2 is great if you want a more traditional MMORPG.

Super Monday Night Combat (SMNC) is definitely my favorite, though being a BIG Star Ward dork I have a soft spot for SWTOR too.

Warframe.

World of tanks for sure
and War Thunder is good too

This question again, uh? ^^
Anyway, Path of Exile for sure.

very recently I've been playing a bit of Realm of the Mad God
I also on occasion will play some Gotham City Imposters