Dallas Semiconductor sells temperature loggers as part of their iButton
line which can be placed wherever you want records. They come in a can
about the size of a quarter. You can also purchase a USB interface,
which you can connect the temperature logger into to get the data out
of it, and set the parameters to sample the data in the first place.
See http://para.maxim-ic.com/cache/en/results/4872.html for the USB
interface, and http://para.maxim-ic.com/cache/en/results/4871.html for
the loggers themselves.

Starter kits are available from
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2820; this kit for $60
includes the USB interface, and a thermocron (which might be for the
wrong temperature range). The thermocrons typically have a 10 year
lifetime.

I've strapped these to water heater output lines and watched the usage
patterns of hot water. Software for windows XP is free for download.
If you're trying to use this with Linux, try the "One Wire File System"
software.