Ideally, you should look for refresh rates of 85 hertz or better. You could buy four of the latter and have more than three times the screen real estate per dollar spent than you'd get with a single 18-inch display. Whichever flat-panel monitor you choose, pay attention to resolution and dot pitch just as you would with CRTs. But because flat screens only work optimally when you're positioned directly in front of them, also consider the monitor's viewing angle, which is the furthest angle away from the monitor's center point that you can move your head before the image fades into a blur. Quality flat screens have viewing angles of 140 degrees or more.
Flat screens come in two varieties, analog and digital.
The analog monitors simply pipe the video information to your screen. The more costly digital monitors encode the information in digital format. The actual encoding takes place on the graphics card. Many people say that the extra cost of a digital monitor and the digital video card that accompanies it simply aren't worth it. The image quality is roughly the same for analog and digital.