Your single-card options are now:
Matrox - they've been doing it the longest
nVidia GeForce2 MX - may have the top 3D performance for single screen games; may not be as functional as Matrox ... yet
Radeon VE - too new to tell; *may* be able to outpace GF2 MX options
Depending on your OS choices, you may be able to use any combination of AGP/PCI cards to drive your displays. Here, I'd say that your performance preferences and wallet will guide you. The second display doesn't have to be flashy as none of its "special" features will be utilized in Windows.
See my dual-display rigs.
-SUO