On my new computer I have an AMD Radeon 6950 which support eyefinity. This is the ability to run 3 monitors (or more) as one virtual display.

In my case this means a display of 5040 x 1049. I have three monitors, all different,

Dell U241o 24” – 1920 x 1200
Samsung SyncMaster 24” – 1920 x 1080
Asus VW222 22” – 1920 x 1080

In an ideal world you would run the same brand model monitor. I would recommend 22” monitors b/c there is not much difference between a 22” and a 24” in terms of what you see, but the physical size of three 22” monitors on your desk is much larger.