The USB architecture is defined as an intermediate speed bus. Clearly, the typical devices attached to serial and parallel ports are excellent candidates for USB attachment. These include most printers, modems, pointing devices, scanners, cameras and like devices. Certainly game paddles, joysticks and steering wheels etc. In fact special purpose game controllers are a natural since they can be connected and used as needed.
Keyboards are now available for USB attachment.
Microsoft just announced a high quality speaker system that supports USB as well as traditional sound board support. The product review indicated that the sounds chopped at times under game conditions on the USB port, indicating a borderline USB attachment candidate. However, under routine computer use USB speakers behaved just fine. USB attached speakers eliminate the need for a sound board in the computer hence they play a perceptively clearer digital sound. Similarly, low end video monitors can be used on USB, while high end graphics will require the use of the internal AGP port and a graphics card.