Brands don't really matter. Every company uses different kinds of panels that most of them don't even make. You should research LCDs a bit before you go out and buy one. tony404 is right about the eizo though, those are really good. I would hate doing any kind of work on a TN panel...
This nec is good and uses a AS-IPS panel...
NEC MultiSync 20WMGX2
Size 20.1" Widescreen
Panel Type TFT/AS-IPS
Native Resolution 1680x1050
Pixel Pitch 0.258 mm.
Color Depth 16.7 mil (8-bit)
Response Time (g2g) 6 ms.
Luminance 470 cd/m²
Contrast Ratio 1600:1
Viewing Angle 89U/89D/89R/89L
Inputs DVI-HDCP, VGA, Composite, S-Video, Component
Other PIP, TV Tuner, Advanced DVM, Integrated Speakers, OptiClear screen coating
Retail Price (USD) $625
Here's small bit of info about LCD panels...
http://en.wikipedia.org/wiki/TFT_LCD
There's some other good info but most of it is on forums at hardocp.com and anandtech.com, they are even stickied, I'm sure you can find it if you want.