I too have used FIREcalc. The problem with using it for me is that we have investments that don't fit in the options, such as real estate partnerships. So I also use calculators that involve detailed information gathering and then do a monte carlo simulation, giving you the odds of success. I like yahoo's money manger for this. You can sign up through http://finance.yahoo.com
. Once you sign in, go to money manger and put in your information. It takes time, but your information is saved and can be updated from time to time.
My 401k also gives us free access to Financial Engines, which does a similar calculation.