Scott from EpicTinker has published a simple explanation of how to simply control Arduino-connected devices via Bluetooth and Android devices. He's used a generic Bluetooth shield with a Freetronics Eleven, and the Android phone is running the popular "Bluetooth SPP" app. After reviewing this tutorial you'll have a solid foundation of controlling devices and can then implement it with other projects. For example controlling a remote-control garage door via your mobile phone, or turning the lights off before going to sleep. A quick demonstration is in the following video:
To get started, visit Scott's project site. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're new to Arduino, the first step is a solid board for your projects - our Freetronics Eleven - the Arduino-Uno compatible with low-profile USB socket, onboard prototyping space and easy to view LEDs: