USB to serial converters, including CDC ACM, Prolific PL2303 and FTDI FT232
Google ADK v.1
PTP with Canon EOS and Powershot extensions, as well as Nikon DSLR cameras
Bluetooth RFCOMM and HID (Sony PS3. Nintendo)
Xbox360 controller over wired USB as well as via a wirelss receiver
Mass Storage Class – USB flash drives, memory card readers, external hard drives/CD-ROMs, smartphones, etc.