Part 3 of the RepRap exhibition. We recently switched to Arduino as our primary microcontroller platform, and we've developed a set of boards based around Arduino. This board is quite useful, and also very cheap. It is a temperature sensor based on an NTC thermistor. It's a very basic circuit, but it is still nice to have a PCB to keep everything nice and tidy. It has screw terminals for the thermistor connection, places for voltage divider resistors and a smoothing cap, and we have a bunch of useful code that will allow you to easily read the thermistor (including a lookup table generator!)
As always, 100% open source under the GPL.