Contrast ratio is the ratio from the brightest color to the darkest color. The higher the number, the more bright a color can be.
Basically it means it's prettier.
RT is how quick the picture on the monitor refreshes. It gives you better performance for gaming.
I suggest this one:http://www.newegg.com/Product/Product.aspx?Item=N82E16824160023
It has a quick response time and 20000:1 contrast ratio.
It has the resolution I would recommend for a 9800GTX+ on a 22" monitor. (1680 x 1050)