The Dell displays have been brighter (that's the 2001FP, 2405FPW and 2005FPW) than the 20" Cinema Display from my own subjective findings. Brightness wise they are on par with the 23" Cinema Display.
The Dell displays have DVI, VGA, Svideo and Composite inputsm 4 port USB 2 hub, Picture in Picture, excellent adjustable stand, monitor rotate if you have an ATI based Mac and use their utilities... Unless you absolutely cannot stand to sit in front of a display with the Dell logo on it, the Dell offerings are better and also cheaper than the Apple 20" IMHO.
I use a dual 2001FP setup and would not have anything else, bright, deep blacks, vivid colour reproduction, fast refresh. Superb displays.
Of course, the best colour reproduction still is to be found on a high end CRT that sadly weighs a ton.
Vicky