If you aren't fussed with 3D gaming performance this one should do the job of running dual displays. Image display quality is pretty much the same across the board for photos, the more expensive cards are really about 3d gaming performance. This ones about £50 and has dual DVI output.
This one would be a better performer with faster memory in case you fancied a bit of light gaming! About £75.
If you wait a few more weeks ATI should be releasing their budget 5xxx series cards which will give you DX11 support, but its not important other than being slightly more futureproof.
Canon EOS 50D/EF-S 18-55mm IS/EF-S 55250mm IS/EF 50mm F1.8 II /Lowepro AW Slingshot 200/ Digital Ixus 860 IS
PC>Q6700/MSI P45 Zilent/6GB 800mhz DDR2/2x 4870 1GB/Samsung Spinpoint F1 500GB/Maxtor 200GB+80GB