Steam free2play games that are not pay2win ?

i played spiral knights for a while and they have a market where you can buy the "real money currency" with in-game gold, and the game is pretty cool if your into it

Dota 2 for sure.

Planetside 2 and Dota2 are the two that comes into mind, Dota2 more than anything, since items bought don't have extra stats.

PS2 has items that can be bought with cash, but i'm not sure they bring extra stats to the game, and either way, they are a bit minusculule considering the amount of teamwork involved in the game.

Spiral Knights.
I read some people saying that is a pay2win game but this is only true (and only in some cases) if you want to play PVP... You only need 1-2 swords, 1 gun and 1-3 armor sets to play PVP and is not necessary having UVs in your weapons.
For PVE you need even less... just some practice killing the monsters.
I have spent a lot of time in that game... more than 2500 hours haha.

America's Army: Proving Grounds - It's still a Beta, but it's definitely free as in free beer.

The Banner Saga : Factions, since you are matched to a same level opponent.