Millions of people have iOS devices at home. Why not use them to control other devices? The IRKit lets you do just that. It is an open source infrared remote that lets you control your air conditioners, DVRs, and lights using your iPhone or iPad. Thanks to the IRKit iOS-SDK, you can create apps to change TV channels, control home electronics with voice, and more.
The IRKit is a Open Source hardware, derived from Arduino. Sets you back under $100.