A Matrox. Hands down best image quality of any video card available. Has plenty of power for you as well. Honestly, I havent personally used a Matrox in one of my machines in a long time but since you dont need much gaming power or rendering power forget NV/ATI. Everytime I see a Matrox running I can call it out by looking at the screen.
You cant top Matrox IMO. As far as specific card, I havent bought one long enough to know. Probably cant go wrong with a surround view Parhelia (3 monitors working in tandem).
If thats not a "workstation", I guess I dont know what one is

Parhelia is not cheap though.. but then again.. it is not *cheap*. You get what you pay for.
If you dont go that route, I could only suggest a cheap NV card like a GF4MX.
Why? I say this because you can run as many monitors as you wish in Windows with multiple PCI based Geforce cards. Nvidias software for multimonitor is the best out there, only probably topped by Matrox's but I wouldnt say Matrox is the hands down winner.
I know you didnt ask for multimonitor.. but sounds like someone with your interests -might- be interested in something like that..
heck, if your doing work as described.. I'd get something that can be, or is good with multiple monitors, or at very least... the best 2D quality that modern video cards offer.