Fire Starter is a one of my first apps. Basically it has a background thread that runs the CPU in the phone to make it hot. It also has a TON of ads because working the radio generates a lot heat in most phones too. It monitors the battery temperature so it wont do any damage to the phone. Surprising its one of my most popular apps, even if its one of the silliest.
If you don’t have access to the Android Market, you can download Fire Starter here.