16 MS is a good response time (the lower the better). Most gamers say this is adequate to prevent ghosting and tearing. You will have to look around for some good models in 19" with a 16 MS, but there are some good ones out there.
As for contrast ratio, 500:1 or higher is best. Lower ratios cause darker shades to be displayed as black, which is not good for gaming.
If your graphics card supports it, you'll want to make sure the monitor has a digital interface (DVI).
Make sure that the LCD's native resolution is the res. you want to use, since the image will not look as good at other resolutions.
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