For Dual Display it's hard to get much better than the Matrox Millenium P Series cards. Though not 3D speed demons they're still fast and the quality is breathtaking. Unlike many dual-capable cards where the quality and refresh rate of the second display are limited these are full bore multi-display cards.
http://matrox.com/mga/workstation/3d...ts/pseries.cfm
Go for the Triple P-750 rather than the Dual P-650 - there's little difference in price and the P-750 is a more capable card. And one day you'll want to add a third display....
Windows drivers are excellent and all us Penguinistas are nagging Matrox to improve their very so-so Linux drivers.