well i noticed in the current Radio Shack flyer that they had a reasonably priced ($14.99) dash mounted Thermometer+voltmeter with remote temp sensor

heres the link (hope it works) http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=&product%5Fid=63%2D1039&site=search&DSUniqueid=3363998 

heres the tiny url http://tinyurl.com/3c8lr  if not goto www.radioshack.com and search on thermometer+voltmeter

anyways this lil gadget has a 12vt hook-up and reads in a dual display either the time, inside temp, remote temp, volts

I plan on hooking one up over my fridge door reading fridge inside temps and aux battery volts. and one on my dash reading outside temps and primary battery volts. 

* Compact design fits almost anywhere in your vehicle�attach with included hook and loop fastener  
* Includes car lighter adapter  
* Backlit display for easy viewing at night  
* Stores minimum and maximum temperature readings  
* Displays temperature in Fahrenheit or Celsius  
* 12/24-hour digital clock  

Obviously I don't have anything to do with radioshack, just passing along a nice cheap gadget.