Somebody else uses and recommended this pet heating pad on another thread recently....
Amazon.com: Snuggle Safe Pet Bed Microwave...
I bookmarked it because I plan on ordering it for the boys. I like the fact that you can warm it up, instead of just relying your pets body warmth to warm it up...although these guys do put out quite a lot of heat on their own.
Ricky(who's always freezing) is like my little heating pad when he lays on me. I can see why they used to put dogs in their sleeves to use as hand warmers in Asia!!