I am currently running an ATI X1900xtx for my game system on a C2D running at 3Ghz.  I mostly play RTS games like C&C, World in Conflict, Supreme commander, etc and like tactical shooters like Far Cry, Ghost Recon, Rainbow 6 and am looking forward to the upcoming CRYSIS offering.  I have dual 20" and dual 24" monitors that I use for my work here at home, but I would like to use them for a 3 monitor game setup.  The plan is to purchase another matching 20" or 24" monitor.  This would make my viewing area 5760*1200 for the 24" setup or 5040*1050 for the 20" setup.  
 
That means I need at least 2 video cards.  For a game like CRYSIS maybe 3 are required.  I currently have an ASUS board that has 4 PCIE slots that runs at 8x per slot. Question is, what can I get away with to have smooth gameplay?   I do not think SLI or Crossfire would work well here since I want to work with 3 monitors. BUT some games CAN be run in a window that I assume you could stretch over 3 monitors. I am not well versed in the capabilities of what SLI/Crossfire can do well under circumstances like this.  But the amount of pixels to be pushed will be high.
 
1. try to pick up another X1900xtx  
2. buy 3 new cards  
--A. 8800GTS
--B. 8800GTX
--C. HD2950PRO (10.1 compatible)
--D. other cards or senarios  
 
I love and prefer ATI for a number of reasons but am not locked into them.  I use a number of monitors in my work so this machine would serve a dual purpose but the higher end video cards are NOT required in my line of work.
 
Any help and insight appreciated.
 
Thanks

For multi monitor gaming you should looking to the TripleHead2Go from matrox. Its a break-out-box that you connect between your video card and your 3 monitors. Most games don't have native multi-monitor support, but Triplehead2Go apparently makes it easy.  
 
http://www.matrox.com/graphics/jp/ [...] g/list.php
 
Is a partial game list.
 
Now since your running 3 times as many pixels on the 3 monitors you'll want the best video card you can get probably.
There are a coulple down falls to the TripleHead2go, such as the resolution isn't very high ... 3 X 1280 x 1024 so its 3840 x 1024 in total at 60 hz, 75 hz requires 1024*768... even lower. Also it only takes standard analog svga inputs.
 
Regardless of the negatives i think 3 monitors would kick @$$.

There is a digital edition of TripleHead2go out now: TripleHead2Go Digital Edition

I don't believe I've heard of anyone gaming at 5760*1200 resolution (6.9 million pixels)