maxmor89, like you, I'm waiting for someone to write code for other USB devices.
As far as I know, anything can be emulated, but writing the code is too complicated for me.
What kind of devices did you think about ?
For example an usb flash drive is not very usefull. The EEPROM is very small, perhaps too small for a FAT file system. Using an SD shield with SD card is of little use, since the SD card itself can be removed and placed in a PC.
A game console already exists : http://arduino.cc/en/Main/ArduinoBoardEsplora
But I looks as if it emulates a keyboard and a mouse, and not a game console.
An audio in and out could be useful in a few situations.