Sensor for ultralow (to -85°C) freezer monitor
The forward voltage (\$V_f\$) of a diode at a small constant current is often used to measure low (cryogenic) temperatures. Silicon diodes have a \$V_f\$ which is nearly a linear function of temperature over a wide range, with slope approximately -2 mV/K. There are even specially-built diodes standardized to specific \$V_f\$ vs. T curves. If you're willing to do a two or three point calibration yourself, then you can use an ordinary signal diode. Even a 1N4148 can accurately measure liquid nitrogen temperatures if you calibrate it.

You can improve accuracy by:


using a stable constant current supply
using separate pairs of wires to supply current and measure the voltage
using shielded twisted pair cabling
applying an appropriate scale and offset to the measured voltage before feeding it to the ADC