The BEST display for gaming is the soon-to-be-released ASUS G-Sync Swift for $800 (2560x1440).
http://www.anandtech.com/show/8085/asus-rog-swift-pg278q-launched-1440p-144hz-panel-with-gsync
It's a lot of money, but I'd far rather have that monitor with a single GTX780 than 2xGTX780 with a low-res, non-GSync monitor.
More info:
https://www.youtube.com/watch?v=3PJjhBUSuHk
and
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/64586-week-nvidias-g-sync-monitor.html
2560x1440:
G-Sync aside for the moment, it's simply awesome to game on a high-res monitor. Games with smaller HUD/Text elements look far better (SC2, CIV5, Diablo III, Company of Heroes, etc..). I still game at 1920x1080 for many games that don't look much different, however even for those the larger 27" makes a big difference and the extra pixels help even if the game resolution is lower.
If G-Sync doesn't sound amazing, you probably don't quite understand the technology.