Dot pitch is the distance between each pixel in millimetres. You can work it out yourself if you know the monitor's horizontal resolution. For wide-screen monitors, the width of the display is about 84.75% of the diagonal size (80% for a non-wide-screen), so a 19-inch wide-screen is actually 16.1 inches wide. As an inch is 25.4 millimetres that's 409mm wide. If it has a resolution of 1440 x 900 then it has 1,440 pixels in 409mm, so the dot pitch is 409/1440 = 0.28.
You can boil that down to this:
For wide-screens, dot pitch = (monitor size) * 21.5 / (horizontal resolution)
For non-wide, dot pitch = (monitor size) * 20.3 / (horizontal resolution).
For colour, an important thing to bear in mind is that most 'consumer' LCDs are just designed to look nice with a computer desktop, games and videos. Most cannot display a full range of 24-bit colours as they have only 6 bits per pixel rather than 8. If you want good colour accuracy - such as for graphic design work - you're going to need to pay a premium for a professional-grade monitor, or make sure that you buy a consumer-grade one that has 8 bits per pixel.
I found
this article which is short and succinct and discusses the differences between 6-bit and 8-bit panels and whether it really matters.
'Contrast ratio' is a rather woolly term that is supposed to be a measure of how much brighter the brightest white is than the darkest black, so a contrast ratio of 2000:1 means that the brightest white is 2000 times brighter than the darkest black. But that could mean 1) the brightest white is
extremely bright but the darkest black isn't all that black; 2) the darkest black is very very black but the brightest white isn't enormously bright; or 3) something in between!
You need to make sure that it has good enough contrast to distinguish shades of dark colour. You can do that by eye or by reading a good review from a trustworthy source. I have two LCD monitors at home - the cheaper one looks vibrantly colourful but in the shadowy areas of photographs, for instance, you can't make out much detail. If I drag that photo over to the more expensive monitor suddenly detail will spring out that couldn't be seen on the cheaper one.
My main monitor is a Samsung 225BW, a 22-inch wide-screen with an 8-bit panel. I'm very happy with it.
If you want to make sure you buy an LCD that meets your needs you have to do two things: 1) do some research to narrow down the choice of models; and 2) view them before you buy one.
Regards
Nelviticus