Personally, I use a pair of QNIX QX2710's. They're nice, fairly cheap monitors and I'm able to do 120Hz on them pretty well, with only two drawbacks: One of them tends to buzz when displaying certain images at 120Hz (doesn't happen at 60Hz), which is fixable, but I'll have to disassemble the monitor fix it. The other drawback is that they have a slight image persistence problem at 120Hz.
Also, I have a friend with a Yamakasi Catleap Q270 2B (the 2C will not handle 120Hz) and he says it works pretty great.
We both bought ours through eBay user green-sum. He's friendly and ships fast.