Connection Options / Connectivity
Most NVIDIA cards come with one VGA and one DVI connector. A DVI-to-VGA adapter lets you use a second CRT monitor as well. Things are more difficult if you're planning on using two digital TFTs (2xDVI), as only very few companies offer cards with two DVI interfaces. If this is what you're looking for, you might want to check out the product lines of Gainward and XFX .
Radeon cards usually offer a combination of one VGA and one DVI output. Again, you can use a DVI-to-VGA adapter to hook up a second analog CRT to your card. So far, we don't know of any Radeon-based cards that offer two DVI connectors. Only ATi's workstation boards come in such a configuration.
Cards By Other Manufacturers
Matrox is considered the market leader in the multi-display field. Its Parhelia and P-750 cards offer connectivity for up to three monitors. Unfortunately, these cards are largely unattractive to gamers due to their high price and poor 3D performance in modern games.
SiS' Xabre and the new XGI cards use a separate SiS301W processor to support multi-monitor functionality. This chips slow RAMDAC and poor image quality greatly limit its usefulness, though. Lastly, we don't have enough hands-on experience with S3's new Deltachrome cards to make any statements about them.
A FS gamers dream comes true - this needs a little more effort than just a dual-display card...
There are only very few "real" multi-monitor games available right now. At least most games allow the player to extend the view port to the second monitor. Matrox christened this mode "SurroundGaming". Sadly, after the initial atmospheric wow-factor wears off, the gamer is left with no real benefit, as this mode would require three monitors for effective gaming.
Matrox has a more or less complete list of games that support this mode over on their website . Cards need to support horizontal spanning for these games, which only the Matrox and NVIDIA cards accommodate.
Simply expanding the view port is not enough, however. Additionally, the field of view (FOV) has to be adjusted. Otherwise, the scene would just be stretched to fit two monitors. If a game doesn't offer an option through its menus, a manual entry in the configuration files or through the console is required. The Matrox website mentioned above lists a few helpful tips for a number of games.
Games that truly take advantage of multi-displays are even harder to find. The most well known are Egosoft's X2 - The Threat (since v1.1) and Microsoft's Flight Simulator 9 - A Century of Flight.