Heat sensitive, colour changing film

http://www.tme-france.com/en/catalogue/detail/cat-16/tech-42/150-Thermex.htm

Or look at http://www.omega.com/toc_asp/sectionSC.asp?section=F&book=temperature

Here's another good one:

http://www.hallcrest.com/

They have a whole line of thermochromatic stickers that you can simply place where you want them.

You might ask Kodak about their Infrared films.

http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=2608&pq-locale=en_US&_requestid=4045

Bobguz

Another option is the Tempilstick (SP?) It's a heat sensitive crayon. Just mark the surface you want to monitor.

Check out thermographic cameras on Wikipedia. There is an extensive selection of forward looking infra red (FLIR) cameras available to cover any temperature range of interest. You can record the data digitally or print it out as a thermogram in any form that appeals to you. You can also use infrared film in a camera, but the temperature range is restricted, and it is more difficult to calibrate.

Thanks to you all. These links are great.

Simon