A lot of people with 3 monitors are going with sli/cf to handle all of the pixel pushing. That said, there are sometimes driver issues. However, if you are going to be playing a game like BF3 on three HD monitors, you almost have to go with two video cards for decent frame rates.
You're going to want to get that x6 to over 4.0ghz or I recommend a 2500K.
Addressing the question in the title about which monitors to go with....
I personally like Dell's line of Ultrasharp monitors. They consistently review well, rotate 90 degrees in their stands (if you like three portrait oriented monitors, which many do, this is key), and have displayport inputs, which really helps with Crossfire setups. Also they are IPS panels.