Temperature sensor for Raspberry Pi (-100°C to 0°C)

Hi all,
I would like to monitor the temperature of a -80°C freezer with a raspberry Pi and have a hard time finding a temperature sensor that can measure temperatures as low as -100°C. All I can find ends at -40 or -50°C.
I have seen a temperature monitor that someone had built with a raspberry Pi for measuring liquid nitrogen temperatures, so I assume there must be sensors commercially available ...
Maybe I am looking for the wrong keywords? Can anyone recommend a digital (or analog) sensor that can be used with a raspberry pi or an arduino?
Thanks!

You might have a look here?:

Thermocouples -


RTD -



Regards, Dana.

A low cost solution may be this.

Mike.

And related to Pommie's post http://www.temperatures.ru/pdf/S&A_2001.pdf - I have opened it and it is safe.

Awesome! Thanks a lot!
I was looking for one and now I have to choose one. ;-) Thanks a lot!