The best I've found is: http://www.financialengines.com

Its free to for feds. As you register and "Select what kind of user you are," you'll see categories forFERS and CSRS. A federal agency must have paid forus to use this system. I have no idea why it hasn't been publicized by the TSP or OPM.

Be warned that it takes a while to enter your information. You can even include Social Security Benefits, a spouse'sIRA etc.

Forbes gave the site a Best of the WebAward (http://www.forbes.com/bow/b2c/review.jhtml?id=6072), but I that may have been a few years ago.