http://arduinotronics.blogspot.com/2010/11/ds18b20-digital-thermometer.html), and have built many projects around it including thermostats and process controls. Unfortunately, the new Arduino 1.0 software upgrade did not work with the older One Wire and Dallas Temperature Libraries. Never fear, the folks at Hacktronics dug up the upgraded libraries, and we just finished testing them with the old sketches. Everything once again is wonderful!
Both at http://tech.groups.yahoo.com/group/arduinohome/files/temperature%20controlled%20solder%20/
Get the DS18B20 at http://www.hacktronics.com/Sensors/Digital-Temperature-Sensor-DS18B20/flypage.tpl.html