Here's a fun gadget that I totally don't need: a USB typewriter that will turn an iPad into a fake piece of paper. From Wired's Gadget Lab:
It holds an iPad in its carriage whilst simultaneously inputting typed letters. All it needs is a Bluetooth component to replace the cable, and a writing app that can use the accelerometer to detect a carriage return and move you to a new line. Ding!
Inside there is a sensor strip under the keyboard which detects the key-presses that hit it, and this pulse of electricity is then passed on to an Arduino circuit-board whereupon it is translated into a standard USB key-down event. All you need to do is plug it in and type.
$400 buys you a pre-modded typewriter, but Jack Zylkin, the man behind the USBTypewriter, will sell you the electronics to make your own for just $75, or you can send him your typewriter and have him fix it up for you. For true geeks, the design can be had for free under a Creative Commons license and you can roll your own from scratch.