Just a quick update here… I tweaked the Commute Cost Calculator a tiny bit. Now the Cost of Commute column also shows how much money was saved for days that were biked. As you can see below, this is depicted by a negative dollar value. The other benefit that comes from this is that the Total Saved Biking value is much more accurate because it is calculated using the varying daily gas prices instead of the monthly average.
The newest version can be found here on my skydrive.