If you are looking to run two larger sized monitors (20+") I would suggest running them off of DVI if possible. Check for a video card that has two DVI out connectors and they should be capable of running two monitors side-by-side. I prefer nVidia video cards personally, I've never had difficulties with any of them. For the price, AMD/ATI graphics are very good though, no doubt.
If you are doing design work, I would suggest looking at the nVidia Quadro line of professional video cards. They are built specifically for that type of work, and while they may cost slightly more than matching desktop counterparts, they offer better support, better compatibility with designing software and tasks, and still all the bang that you could possibly need! I've built numerous computer systems running the nVidia Quadro FX570 card.