Hifiduino: project blog by The Lazy Engineer chronicling his work to build a very slick Arduino-based hi-fi remote control. I especially like the casing work-- nicely assembled wooden box with its top made from an aluminum hard drive housing; one of the best uses of scrounged hardware I've seen. He has also chosen a lot of technologies I've been exploring in terms of (1) making an elegant interface with a single rotary encoder and display, and (2) using I2C chips for easy interfacing. The blog "extras" on the right are an excellent example of sharing, too, with links to code, examples, references, etc.
Paperduino: an Arduino circuit design by Guilherme Martins for introducing Arduino to neophytes in a workshop setting by having them build one from raw components on a 2-sided color printout. Beyond looking cool, it helps to get over the "soldering is hard" issue (pssst-- it's easy and fun!) and to understand the minimal necessary components to make a working Arduino circuit. Flickr set from the workshop, Paperduino PDF patterns.