This was the most comprehensive web-based home-energy audit tool I could find, especially if you use electric/heat pump source (didn't try it for other sources, but it accomodates LPG and NG):

http://hes.lbl.gov/

Disappointingly, there is no real way to include "hybrid" heating sources (eg heat pump + resistance aux heat + propane fireplace). You have to lump all sources as a single BTU figure. My heat pump is 3 ton (36000BTU/hr) with a 15KW aux heater (51000BTU/hr). The cost of the 1st 36K BTUs is way less than the cost for the last 51K, but all 87K are calculated as though its heat pumped.

This lack of granularity is in contrast to the ability to individually enter each and every lighting fixture and appliance in the house!