The largest pixel count I have ever found on a monitor is 2560 x 1600 for the Dell and Apple 30". Haven't seen 3840. Granted, I have been using my Matrox TripleHead2Go and DualHead2Go devices to output 2x1920 but never on Catalyst and never in a show environment.

I use Dell monitors (the cheap ones) just as confidence monitors. I was able to buy a whole bunch of them from the factory outlet for only a few hundred USD. The refresh rate sucks and the pixels are fuzzy but they are also not something I depend on.

The BenQs Simon mentioned or Apple Cinema Displays, even the higher quality Dells are find and tend to be the ones I use for more mission critical work. Still, the issue is to evaluate what your needs are and if all you need is a quick view to verify what you're putting up on the stage then buy cheap. This way you won' be hurt as much when someone breaks one.