I use a Dell U2711. Best monitor I've ever owned. Reviews say noticeable input lag, but I've never noticed any and I'm a fairly hardc0r3 gam3r.

More to the point, I'm a graphics programmer / researcher, so monitors with low Delta E are important for my work. The Dell U2711 combined with an i1Display Pro can be calibrated to exceptional color fidelity.

I have an HP LP2475W and a Dell U2412M; generally, among the IPS class, the consensus seems to be that HPs have more outputs and a better UI. Some of them are wide-gamut, however, which turns off a few purchasers. Research as to whether or not wide-gamut is important/detrimental to you.

I'd say go for 24s or a 30; if you have the 27 you'll just wish you had the 30 :-p but definitely go IPS, they are fantastic. I haven't read much about the Korean monitors as they were nonexistent when I researched the market 4-5 years ago.

Actually, the Dell U30xx is worse than the U27xx. The color fidelity isn't as good. (This only matters if you calibrate your monitor.)

I've been pretty happy with my NEC monitors.