You could try signatrol.com. They do a range of data loggers both for sale and for hire. I have a set of SL52T temperature loggers which are very easy to use.

Yes Homechip, ask for Ellie and give her my regards.
You will need either the combined temperature/humidity logger:
http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=47&osCsid=3c8382a27df3adc80b1d4a639412310b

or if it is just temperature (and I have taped a few to a body to see what happens during the day) then the basic http://www.homechip.com/catalog/product_info.php?cPath=21_31&products_id=33&osCsid=3c8382a27df3adc80b1d4a639412310b

You will also need the reader:
http://www.homechip.com/catalog/product_info.php?cPath=23_28&products_id=39&osCsid=3c8382a27df3adc80b1d4a639412310b

and an adapter:
http://www.homechip.com/catalog/product_info.php?cPath=22&products_id=30&osCsid=3c8382a27df3adc80b1d4a639412310b

You can download the software.

One word of warning, when you are not using them make sure that you disable the mission, I left a mission going for a couple of years, on rollover, it was logging every minute and flattened the battery.

Apart from that they are very useful and easy to calibrate if you need to.

They claim a million samples, that is why turning them off is important when not in use.
Mine must be 5 years old and half are still working. I have been a bit rough with some of them, one I over heated and the case 'popped', it still works, a couple of other I put in hot water for weeks, they did not like that.
At a tenner each though it is not that costly to replace them.
The software is pretty basic and easy to follow: You can set up the sampling rate, C or F, a delayed start, set the clock to the PC clock, set a low or high alarm and the important thing is that you can save the data as a text file and play with it in a spreadsheet later.