It depends on your use. If you care more about response times than image quality, go for one of the fast TN panels, such as the BenQ FP93GX.
For general use, if you don't mind going WS, one of the best panels is the NEC MultiSync 20WMGX2, although, it's a bit on the expensive side.
The HP LP2065 also carries an S-IPS panel, like most Dells. The above 2 are pretty nice also.
There's a knowledgable person over at
Anandtech that's been reviewing monitors and fielding questions.