I've also seen good monitors from dozens of different companies. Keep in mind that you will be spending hours staring at this screen. Your best guide is your eyes. Pick a monitor that looks sharp and clear, and you will be happy with it. The monitor that comes with your computer is usually 15 inches and of good quality.
Many computers come with a monitor already included.
Sometimes these monitors are good, and sometimes they're awful. Look and see for yourself. Compare the monitor that comes with your computer to the others available in the store. If most of the monitors look better than that one that is included, talk to a salesperson about getting a better monitor. Sometimes they can do something.