Dell Ultrasharp U2410.
Absolutely phenomenal monitor. Unlike the Apple Thunderbolt Cinema display, it has HDMI, so you can hook up other devices to it. That to me, is the deal breaker along with an audio out port to hookup a proper sound system to it. I very much doubt Apple's display does any better than tin canned crap sound quality out of those built in speakers.
For the price that Apple is asking for the Thunderbolt display, it should come with HDMI and audio out and a few extra goodies (sd/cf card reader, especially CF for professional use, ie photographers like me who would benefit from a big display and great panel).
Onto the Dell, its 24 inches, IPS, comes with a plethora of connectivity:
And if you can get a deal good enough on it, you can score the beauty for $600, signifcantly less than the Apple Cinema display.
The other monitor I would recommend:
Asus P246Q
Basically, its the same rebranded panel that the Dell Ultrasharp U2410 is using, but with a few extra goodies. It has a REALLY sweet function where it overlays boxes you can select from 8x10, 11 x 8.5, etc on top of the screen, giving you the ability to measure up the size of your document BEFORE its sent to print.
Its price is usually $500.
More specs on the Asus here;
http://www.amazon.com/Asus-PA246Q-24-LCD-Monitor/product-reviews/B004NBZ994
I had the Asus, but needed to return mine as I kind of bought it on impulse when I'm lacking the funds (being a student sucks). Its a great monitor though. Very bright with vibrant colours.
http://www.amazon.com/Asus-PA246Q-24-LCD-Monitor/dp/B004NBZ994