Just use a J, T, K, or S type thermocouple and a level converter IC.
The level converter can be found here. I suggest the LM135 in the TO-46 Package. This will allow you to read in temperatures of -50C to 150C off of one of your analog inputs.
The temperature is read off in kelvins, with zero kelvin being zero volts.
Calibration routine found here.
I used a thermocouple/level converter for a science project back in 7th grade, these things work great and are very rugged. Simple circuitry too.
If you need help just let me know.
-Q