I have used use ColorEyes Display Pro for the last couple of years. I just set it up for my new 27" iMac and for my 4 year old Cinema Display 23" monitors.
There are a lot of opinions regarding calibration software and (because you asked )I would strongly suggest investigating this company before making a decision. I did a lot of research before choosing a calibration system and think ColorEyes is superb. They don't advertise as much as some of the more popular systems, but it is my belief that they are the "best" in the under $ 1,000. category.
A friend of mine uses it for his Dell monitor with equally stunning results.