This display offers a 1920x1080 resolution, a 21.5 inch viewing area, and is available for only $189. It has a DVI and VGA port, which means that you might need an adapter to connect it. There's also a 24 inch model of this display, the Dell ST2410, if you're looking for something a little bit bigger.
If you're wanting another option, there's the Samsung XL2370. It's LED backlit, like the Apple LED Cinema Display, and can be purchased for around $399. It has a display resolution of 1920x1080, and it features a DVI and HDMI port, so you'll need an adapter to hook it up to a Mac with a Mini-DVI or Mini DisplayPort.
Apple LED Cinema Display
The Apple LED Cinema Display offers unique features that make it easy to connect to a Mac, like the MagSafe connector that charges a MacBook. The display is measured at 24 inches, and can display a 1900x1200 resolution. It also features a built-in iSight camera, a mic, speakers, and a three-port USB hub. You can purchase it for $899, though refurbished models have shown up for $599 from Apple.
27 inch iMac
The 27-inch iMac, can be used in Target Display Mode as a monitor for another Mac with a Mini DisplayPort. It offers a resolution of 2560x1440 pixels, and it's LED backlit. You'll just need a cable to do so, and you can purchase a Mini DisplayPort to Mini DisplayPort cable from Apple or Monoprice. Of course, the iMac is a computer, so we aren't suggesting using it primarily as an external display.
Do you have any suggestions for displays? Leave a comment and let us know!