to OP. if its a single card you are looking for, then you have to either use:
Amd card with display adapter(except Sapphire Flex) for 3 or more monitors
Gtx 600 Series card. Amd tends to work better on multiple screens
3d: Nvidia is more prefered, as their suite for 3d is well more developed as AMD had just got into 3d business and its pretty new, so it will be awhile till its actually ready to use by a larger majority.
Physx: only found in Nvidia cards.
Crossfire/CFX/Sli: just about all cards will have it except really low end ones and a few select models
My personal recommendation is a Gtx 660, or a HD 7870
my mb is asus m5a97 r2.0. itr supports only crossfire x.or tell me a nvidia gc. in budget below 300$ with sli and with oc capabalitiss.
later i'll buy new mobo with sli. my processor is amd fx 8120.cooler master gx650 smps