One of the lesser-known eco-mods seems to be grill blocking - the covering of openings on the front of the car, as with tape or stiff plastic or some such.

Just saw a TV add from the Dodge Dart which shows that it has automatic adjustable grill blocking. Pretty darn cool if you ask me. Although, if you asked me follow-up questions I would likely be pessimistic about how well this would work with winter and ice and freezing rain, all of which would call for a blocked grill anyway.

http://www.greencarreports.com/news/...lp-improve-mpg