'They' recommend that you have a refresh rate of at least 75 Hz to reduce eye strain, but I also like to use @ at least 85 Hz.
The refresh rate is usually determined by the resolution you will be running the monitor at. Personally, for a 19" monitor, I feel that it should at least support 85Hz @ 1280 X 960 (or 1024). The monitors listed in your other post all meet this except for the Samsing 955df which officially supports only up to 75 Hz.