Check this monitor out: Viewsonic VP2290b
This monitor is really made by IBM (T220, T221) and they are the same as far as I can tell.
It's incredibly expensive, requires a special, dual DVI video card, and only supports 30Hz refresh (no biggie, it's LCD) but it's hard to beat 3840x2400, 200 dpi resolution. You can view 6MP files at 100% in Photoshop with room to spare.
Editing images on this monitor is incredible. You can see literally everything.
