I'm going to but a nvidia 660, but I don't know whether to get it by Asus or eVGA.
Both are really nice, i would get the Asus, runs a bit cooler under full load. But MSI TF III has even lower temps, and is cheaper here, so i would get that instead.
For that price, you are much better off with a 7870XT. It will beat the 660 (non Ti) in practically every single situation, ever. Stick with AMD for graphics cards; they are the only card to use for mining Bitcoins, Litecoins, Mincoins, etc. and are cheaper for equivalent or more performance.
That's what I have. No complaints with it so far; I've had it for about 4 months now. I OCed mine a little and I can just max out the new Tomb Raider. Most other games run pretty nice too. If you are willing to get another 660 down the road in SLI, it'll be faster than a 680 :D