If you are interested in Google' ADK
(Android Open Accessory Development Kit), but Feeling ADK Developer Mage2560 is too expensive. The USB host is you best choice. We recommend assemble with our Freaduino v1.0 with ATMega328
(100% Arduino compatible).
USB Host Shield is an add-on board for Arduino development platform and contains all of the digital logic and analog circuitry necessary to implement a full-speed USB peripheral/host controller with your Arduino. This means you could use your Arduino to interface with and control any USB slave device - thumbdrives, digital cameras, bluetooth dongles, keyboards, mice, joysticks, MIDI, and much more!
A four-wire serial interface is used to communicate with the host controller chip, so the shield connects the Arduino's hardware SPI pins (D10-13) to the MAX3421E. A USB type A female connector is wired up to the IC, and it also supplies 5V as any normal USB port would.