Now here is something you don't see every day.  A thermoelectric device every cat should have.  I'll let the citation and abstract speak for themselves:

Sethumadhavan, S. and D. Burger (2006). Powering a Cat Warmer Using Bi₂Te₃ Thin-Film Thermoelectric Conversion of Microprocessor Waste Heat. Twelfth International Conference on Architectural Support for Programming Languages and Operating Systems - ASPLOS XII. San Jose, CA USA.  (pdf) (ppt)

Introduction

New thin-film materials offer potentially greater efficiencies
when converting heat to electricity using the thermoelectric effect.
Applied to microprocessors, this technology can mitigate
a number of critical problems in one fell swoop: the dangerous
amount of heat produced by laptops [14], [17], climate-change
inducing electricity consumption [11], and unhappy house-cats
that are insufficiently warm [1]. Figure 2 depicts an apparatus
that addresses these three problems comprehensively, by extracting
waste heat from a high-end microprocessor, converting
the heat to electricity using thin-film technology, and using the
resultant current to power a portable cat warmer.

This paper was presented at the above conference.  Seriously.  See this link from the conference program:

http://www.princeton.edu/~asplos06/waci.html

The author is an assistant professor of computer science at Columbia University.  Here is his homepage:

http://www.cs.columbia.edu/~simha/

The full paper (pdf) and powerpoint presentation (ppt) are available online.