ST2420L is history, look for S2440L at similar price (13-14k). Its VA panel upgrade from the TN panel of the ST.
U may also check S2340L or S2240L, both got IPS panel and should be priced somewhere like 9-11k. Just forget the ST series, they had some issues, and now out of market for good.
I bought a ST2320L in Jan 2011, and this monitor went kaput 2 times in a year, and finally Dell replaced it with a S2440L this January (2nd replacement). This monitor is a huge improvement over that ST, but not without issues, screen goes dark when a light/fan switch is made on/off in the switch board. Not sure where Dell's product quality is heading, but their customer service is awesome, u will get immediate replacement if within warranty and product is physically intact.
When using high res monitor, better use DVI or HDMI cable, I find images crisper with them from a normal VGA cable.