I don't commute, but I did it for my husband. Prett cool tool...

http://www.state.nj.us/transportation/commuter/rideshare/costcal.shtm

Interesting! AAA publishes an annual report on the cost of driving, and their estimated average for 2006 is 52.2¢ per mile:

http://www.aaapublicaffairs.com/Main/Default.asp?CategoryID=3&SubCategoryID=9&ContentID=23

It's pretty close to what the NJ calculator told me.

Wow, that is disturbing knowledge to have. I sure wish my husband didn't have a 70 mile commute 6 days a week.