I did a quick search and found this color blind simulator, where you point it to an image on your machine to see how it would look to people with various types of color-blindness. I just gave it a cursory glance, but it might be worth looking into. I've seen/heard of similar sites in the past.
One that I use frequently, that I feel works really well is ColorOracle.. Like Dave mentioned, there are several out there - but ColorOracle was made by a cartographer!
Does anybody have a sense of whether or not the built in Illustrator colorblind simualtor is less robust than these online versions? Should I be looking beyond illy for this or do they simply duplicate each others results?