Get visual feedback from your Pi!
The PiGlow is a small add on board for the Raspberry Pi that provides 18 individually controllable LEDs. You can use it for all sorts of things! And of course, it fits inside a Pibow!
There are tons of things you can do with it:
This board uses the SN3218 8-bit 18-channel PWM chip to drive 18 surface mount LEDs. Communication is done via I2C over the GPIO header with a bus address of 0x54 (Python example code provided). Each LED can be set to a PWM value of between 0 and 255. Comes fully assembled and ready to rock.
Pimoroni PiGlow (3:55)