ngourlay:
I'm rather late to the game, but I was searching for in-car solutions, and found this:http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1953161_-1
Vin 9-18V, Vout = 12V
good find.
We have an other thread about improved power-supply rejection;-
http://forum.arduino.cc/index.php?topic=162326.msg1276774#msg1276774