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!