You will need:
- Temperature sensor, such as the TMP36
- Relay or RC plug switches
- Screw terminals
- Box to trap the heat
- Heating/cooling element, or incandescent bulb with fixture (or both)
Using just an Arduino and a few parts you can create a temperature control device instead of paying for a commercial model. Not only is this an excellent beginner level project, but it has real-world applications!