If you are looking for the most accurate colours then you will want to get something with an IPS panel like the first $500 Dell that was posted. There is also the Asus PA246Q at the same price and with a quick google search it seems the Asus is just a bit better:
http://www.amazon.com/Asus-PA246Q-24...5628628&sr=1-1
If money really isn't an option then this NEC is the best one on the market:
http://www.necdisplay.com/p/desktop-...cd2490wuxi2-bk