My CycliStats program includes a built-in calorie and average watts calculator. It takes into account rider weight, bike weight, distance, speed, rider position on bike, elevation gained, etc. (it sounds more complex than it is...the calculation is pretty much automatic when you log a ride in the program).

Here's a link that shows a screen shot of the Calorie Calculator: http://www.shastasoftware.com/CycliS...calculator.htm