I think the decision comes down to how large a display you want.
I have a 27" Samsung LCD TV as my monitor.. (size matters) Max rez is 1360 x 768. With my XFX Geforce 7950 GX2 all games with mazed setting look great, even at that rez.
There are a lot of great 19" LCDs out there that run HD rez nowdays and with impressive response times. Please note, if you want to maximise display quality if you are outputting at HD, you really need to utilise DVI or even HDMI.
Great comparative review over at firingsquad
The monitors mentioned in those reviews are the ones you'll come across most when seraching for monitors used in gaming moreso than anything else.