In keeping with the inexpensive design philosophy of the Raspberry Pi, the designers saw fit to not include a power switch, however this is not an idea situation as abruptly removing the power can increase the chance of data corruption or data loss. With this in mind, Instructables member MrLeeh has documented a neat hardware-based solution based around an inexpensive ATtiny microcontroller.
With a single button the circuit can send a shutdown signal to the Pi, wait for the shutdown process to complete and then remove the power from the Pi - and also act as a power-on button to bring it back to life. Much more conveinent than shuttling USB power cables around and reducing wear and tear on the hardware.
To make your own, check out the circuit and AVR code published in the project's Instructable page. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
If you need to connect external circuitry to your Raspberry Pi such as the shutdown project above, consider our PiBreak board. It provides labelled breakout pins for all GPIOs, a large prototyping area with solder pads, and power rails for easy power connection:
Furthermore the PiBreak also includes mounting hardware to firmly attach it to your Raspberry Pi using a nut, bolt, and spacer - and is compatible with all revisions of both model A and B Raspberry Pi computers. For more information about our PiBreak board, our Getting Started guide, and to order - visit the product page.