Look here:
http://www.performancetrends.com/SuspAnzr.htm
This is the program I use. It is very comprehensive and works well once you get all of the variables plugged in. You can also use it for 9 days for free. I actually designed the complete suspension for my Bad Ast project on the freeware... I just picked up the program a couple of months ago so I could do some tweaking. It's not real cheap but, for what it does, I feel the cost is fair.
Mark