This sketch reads the temperature from a TMP36, and displays it on three 7-segment LEDs, via three shift registers.
It uses the INTERNAL voltage (about 1.1V) as the analog reference, as the
TMP36 only reaches 1V at about 50°C, and I'm using this as a basic room
thermometer.
The INTERNAL voltage on an Atmega 328P isn't exactly 1.1V, so you'll want to
measure the voltage on your particular chip and substitute in the
value in millivolts.
You could use the default analog reference (5V), but then you'll only be able to measure in roughly 0.5°C increments.
When I have time, I'll add a wiring diagram and some additional details.