Well, what a nice piece of junk your pc would be if you had no monitor! There is obviously not much to tell about monitors. In my scale, a good quality monitor should have the following basic features:

1. High refresh rates(75Hz+ at all of your workable resolutions)
2. Ergonomic controls
3. Digital controls; On-screen menu is a bonus

Always go in for a monitor that gives out the maximum resolution for a given size. See table below.
 
 

Monitor size	Max. resolution/Ideal res.@ Refresh Rate
14"(do you want to buy this one?!)	1024x768/800x600@85Hz
15"	1280x1024/800x600@85Hz+
17"	1600x1200/1024x768@85Hz+
19"	1600x1200/1280x1024@85Hz+
21"	1900x1600/1280x1024@85Hz+

Going for a 21" monitor is a bit of a overkill for the home PC users. Serious(& I mean it!) CAD professionals are the only ones who require such large monitors.

Also keep in mind that it is quite common to get a monitor that has a few defects. Typically, look out for moire, colour variance, brightness & contrast levels, and an out of focus picture. Many monitors come with a variety of adjustments, such as degauss, autofocus, colour intensity etc, & some provide on-screen menus also. The choice of these features depends on what kind of work you do, & how much each feature matter to you.

Which is best?
A 17" monitor is most ideally suited for the home PC.

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