robtillaart:
Check the DS18B20 sensor - MilesBurton.com -enough samples to get you up and running!
And it should be pointed out that many of them can be strung together on one OneWire bus and use only one Arduino pin for the lot!
Despite being called the OneWire bus you need Vcc and GND too, so its three wires (there is a parasite mode which uses only 2 wires, but its trickier to get working well I think.)