I've been running dual-head for years under NT and, now, 2000. I, too have had the best luck with the Matrox cards, although the early Appian cards worked pretty well, too (I don't know what their current line looks like).
My Matrox G400 MAX has (in the latest drivers) stability and great functionality, something you just won't find in the other dual-head solutions out there. The Matrox PowerDesk utility allows you great control over the placement and sizing of windows across the monitors: choice of pop-up dialog placement, maximization control (one monitor or across both), window opening placement, and lots of other things. For 2D and DVD playback, I've loved it, and, as a software developer, the extra desktop space affords me lots of interesting uses for editing and debugging. Unfortunately, the G400 is NOT the solution for you if you intend to play the latest crop of 3D games.
About 6 months ago, I replaced my G400 MAX with a Leadtek GeForce2 MX DH Pro. It's been nothing but heartache, too. Sure, the dual-head features are there, but the card has been flaky, flaky, flaky. When it works, the 3D performance has been good; Tribes 2 runs like a dream. Unfortunately, the drivers have made my machine quite prone to lock-ups in games. ALL 3D games have done it, both OpenGL and DirectX 8a. I've been hard pressed to find a solution to it, unloading most everything from Win2K (including the Leadtek WinFox program, which I just don't trust), and changing drivers frequently (both LeadTek and the Nvidia Detonator drivers). Nothing has been particularly helpful. Unfortunately, LeadTek is not the most responsive company in the world, and has not provided many clues to resolving this issue, so I am forced to think of a better solution or return to my G400 MAX.
I've considered trying the Radeon VE Dual-display, but reviews have, thus far, discouraged me. Similar problems with a single-head Radeon DDR (bad Win2k drivers and problems with them on Athlon Motherboards) haven't helped ATI win me over, either. Anyone else have one on Win2k?
You may have better results with the Leadtek card under ME or 98; it appears that most people have. Otherwise, don't waste your time and money with anything but a mature dual-head card. At this point, it looks like I may go to a game-specific machine ALONGSIDE my development box, with dedicated, single-out hardware. I just HAVE to have my games, AND my dual-monitor support, too.