24in Dell 2407FPW @ 1920x1200. Love it, no backlight issues, ghosting, or stuck pixels.
I'd love to go larger and get a 30in panel, but the only video cards that can drive that resolution with the latest games are Crossfire or SLI based solutions. I'm not paying that kind of money. When I finally do replace this 24in panel, though, it'll be a 30in that I get to replace it. Video card technology improves with every generation and a decent single card solution today will be able to drive most of the games I play at its native res. Future cards will do it better though.