Using more than one monitor has a number of advantages, offering a lot of desktop space without the prohibitive cost of the largest monitors. To create an effective multi-monitor setup, you need to follow a few simple guidelines.
Firstly, you need to be able to connect all of the monitors to the computer. Most modern desktop computers offer two outputs, with the most common configuration being two DVI ports or a DVI and a VGA port. Both of these can be used to drive multiple monitors, but the VGA port usually produces lower quality images than the DVI one. Dual DVI ports are preferable, and you should consider upgrading the graphics card of your computer to one that offers this at least if you want to get the most out of your setup.
Although it is possible to use two different monitors together, it is preferable to use two identical monitors, as they are more likely to have matching on-screen colors. However, if you are upgrading to a new monitor, there is no reason not to keep the old monitor connected and use it as a secondary display. That way, you can put less-often used things like music controls or email programs on the smaller monitor, and put the more important stuff on the bigger, newer one.
When choosing the monitors, you should be looking for simple, low-cost monitors to keep the total cost down. If you want to go all-out and have more than two monitors, you should also look at getting a graphics card that supports more monitors. Specialist graphics cards like the Radeon HD5870 Eyefinity 6 offer connections for up to 6 monitors, each running at a resolution of up to 2500 by 1600 pixels. If you were to run that with six 24-inch monitors, that would give you a total resolution of a mind-boggling 7500 by 3200 pixels. It would also give your bank manager a severe headache, as the graphics card on its own costs about $450 before you add in the cost of 6 monitors and the way you mount them.