Be jealous, [H]ard|OCP tested a Radeon HD 6990+6970 CrossFireX setup with three 24" Dell 2408WFP.  Of course, the GPU subsystem its self will run you about $1000 without even looking at the displays.  However if you really have a burning need to play DX11 games at 5760×1200 with everything turned up to max, then this is your best and most economical choice.

Three cards for three monitors, try Tri-Fire - Graphics Cards  1

"What happens when you take an AMD Radeon HD 6990 and add a Radeon HD 6970 to it for 3-way GPU CrossFireX performance? We compare this configuration directly to GeForce GTX 580 SLI a multi- monitor setup at high resolutions. TriFire in all its Eyefinity glory! Along with one new DX11 game."

Here are some more Graphics Card articles from around the web:

 Graphics Cards