I've seen a few different fuel cost calculators online, but I find this one to be the most useful. Very easy to use. Just enter the fuel cost per unit ($ per gallon, cord, ton, etc.) and your appliance efficiency and it will compare the different fuel sources on a per-million BTU basis.
(broken link removed to http://extension.oregonstate.edu/catalog/details.php?search=EC+1643&submit.x=9&submit.y=9)
(broken link removed to http://extension.oregonstate.edu/catalog/details.php?search=EC+1643&submit.x=9&submit.y=9)
