Battlefield 3 shipped with native support for Eyefinity (multiple monitors under AMD hardware), to the praise of the more extreme enthusiasts out there. If you're curious to see what you're missing, the video below from YouTube user nhalberg contrasts what he sees in Eyefinity versus what the average user sees in a single monitor configuration. Unfortunately it's mostly tank gameplay; infantry footage starts at 8:33.
Altogether, the rig running it cost about $2000, but Eyefinity setups certainly don't have to be this expensive. If you're fine with lower resolution monitors and reducing some settings to maintain a high framerate on a single GPU system, one can go considerably lower.