LCD monitors don't really have refresh rates... and the thing they call refresh rates on LCD monitors is nothing but a trick to get people to pay more. There is no difference in image quality between a 60/75hz LCD and a 120hz LCD. This used to be an important factor when buying CRT monitors because low refresh rates would cause the monitor to flicker and a lot of people (including me) would get headaches from looking at the screens for too long. There is a huuuuuuge difference between a 60hz CRT and a 120hz CRT... but with LCD screens.. not so much.
LCD Screens don't flicker unless the backlight is broken or the backlight has a low frequency and you just don't get that in new monitors these days so there isn't any thing to worry about.
tl;dr: Refresh rates on LCD monitors are irrelevant unless you have a specific reason to get a monitor with higher refresh rates
120Hz (and 240Hz, 600Hz) monitors are tailored for Blu-ray movie playback. Blu-ray movies are recorded at 24Hz (roughly), thus a 120Hz, 240Hz and 600Hz LCD/Plasma monitor will minimize choppiness during playback due to it being divisible by 24. Also you can tell a difference (I can anyway) when watching high action broadcasts such as Sports.
120Hz is older technology (excluding 3D HDTVs). Most LCD HDTVs are 240Hz and Plasmas are 600Hz.
Note: When HDTVs are connected to a computer it will default to 59-60Hz. You need to modify the graphic device driver to force a different refresh rate. Usually this can be done automatically when Blu-ray playback is detected.