WhatColor
WhatColor is a small and simple-to-use tool that identifies the color of a pixel on any part of the screen by placement of the cursor. It tells you the hexidecimal number and the actual name of the color. You can even save the number to clipboard by binding keystrokes in the preferences panel. This proves to be quite useful for webpage builders and image designers.
It is shareware - a small registration fee entitles you to free updates for life - but you can operate the program continually past the trial period.
WhatColor is written by Hikaru Nakahara and is currently up to version 4.63e.