For an interesting and somewhat futuristic form of user input, consider the following 3D controller. Using three aluminium-covered squares as capacitive sensors (one for each axis), Kyle McDonald has a very neat system that can roughly determine the position of your hand within the open cube. To take advantage of this, he has included a processing sketch to demonstrate monitoring the controller by a PC, for example:
For complete instructions visit Kyle's project page. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're an experienced Arduino user and interested in more advanced Arduino projects and usage - get yourself a copy of "Practical Arduino" by Jonathan Oxer and Hugh Blemings:
Create your own Arduino-based designs, gain an in-depth knowledge of the architecture of Arduino, and learn the easy-to-use Arduino language all in the context of practical projects that you can build yourself at home. Get hands-on experience using a variety of projects and recipes for everything from home automation to test equipment. For more information and to order, click here.