This Dell U2713HM monitor is one of the best consumer monitors you can buy and Dell's running a great sale on it today. Its primary feature is that it is a 2560x1440 IPS panel—also known as WQHD—and that's a lot of pixels. That's the same number of pixels as the 27" iMac. Not only do you get a lot of screen space, but because the screen uses in-plane switching technology, the color accuracy will be good enough to do design work.
You can compare this beast to Apple's Thunderbolt monitor at $1000 or Viewsonic's version at $780. For $700 today, this individual screen looks like the best value by far of the three. Plus, you're getting it from Dell, which means if there are bright or dead pixels, you can get a new one. Try doing that with a cheap-o Korean monitor from Ebay.