Making your own Android apps to control an Arduino may have seemed out of reach, usually such development requires a lot of coding, experience and time that generally isn't avaliable. However thanks to MIT and Google, there is a simple, web-based method of creating your own - the MIT App Inventor.
To help us get started, Arduino enthusiast Rui Santos has created a video tutorial on the development environment, and follows with showing how to control an Arduino from such an app using a simple Bluetooth link. With the right hardware and the App Inventor, you'll be creating custom hardware-software integration that you never thought possible. You can watch the video below:
If you're looking for an Arduino-compatible board with inbuilt USB host shield in order to connect directly to Android devices, look no further as we have the Freetronics USBDroid board:
Apart from being a fully Arduino Uno-compatible, it has onboard microSD socket and the full USB socket and host-mode controller. This is the ideal platform for developing peripherals or projects based around Android devices with ADK (Android Developer Kit) functionality, but without requiring a USB host controller shield stacked onto an Arduino. For more information and to order, visit the product page here.