Northern tool has a 150 watt oil pan heater. Silicone pad with glue. http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200339139_200339139

This one has a chart to show how many watts you need based on application:
http://www.warehouseautoparts.com/Specials/Kat/Kats_24100_Silicone_hotpad_oilpan_heater.htm

Lots of different heaters:
http://www.warehouseautoparts.com/Specials/Kat/Kat_heater_Specials.htm

They also have other sized. I bought a 25 watt, 50 watt, and a 100 watt heater. I also bought a 60 watt battery heater. You just have to ask.

-Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.