Eyefinity!!!

Hello
A 5870 will do the job fine,however i would recommend going with 2 5870's,because another 5870 will give you a good boost in performance.

^ And to add to that you might want the 2 GB version of the HD 5870, and if you can afford it, two HD 5870 2 GB if you do intend to play @ 5760 x 1080 if you're using three 1920 x 1080 monitors.

+1^ and +1^^

If budget allows, the extra frame buffer will boost performance with eye candy.

i run eyefinity on mw2 with a single 5870 on max settings. you will need to get the widescreenfix however.

haven't had a chance to try dirt 2 in eyefinity yet...