Definately Matrox G450 (possible a G400 if you can get one cheap and second hand).
The G450 comes in Single Head or Dual Head versions.
16MB of RAM is enough to run both heads at 1600x1200x32bit.
You'd really only need 32MB for gaming.
But if you want to go above 1600x1200x32 you'll need more than 8MB per head. Besides the 32MB version isn't that much more expensive, so you might as well get the 32MB Dual Head Version.
Who knows you may get a 24" monitor one day and actually want to use 2048x1536x32
G450 vs G400, the G450's second display is a little more powerful, but the G400 is a little faster in gaming. But since you don't care about that, I'd go for a G450. The only reason I mention the 400 is that it's a little older you might be able to find one cheap for less.
But the G450 is pretty cheap already.
Also others have mentioned the Radeons, they also have very nice 2D, and are also good 3D cards. But even a Radeon LE probably isn't much cheaper than a G450-DH. So I'd go that way if I were you since you don't care about the 3D performance of the Radeon.