Arduino: The main website for all things Arduino: tons of projects, explanations, tutorials, and information here!
Arduino Projects at Instructables.com: Instructables.com is a DIY (Do-It-Yourself) website filled with how-to guides for many kinds of projects. There are lots of Arduino projects there -- some easy, some difficult, and some absolutely crazy -- but they're all interesting!
Arduino-Powered Korean Word Clock: A cool clock you can build yourself!
Arduino Light Organ: Build a color organ that responds to music!
Daft Punk Arduino Helmet: Here's a really cool, but very complicated, project you could build for a Halloween Costume next year: a mask or helmet with a programmable light display in the face.
20 Unbelievable Arduino Projects: A free ebook from Instructables that includes 20 cool and amazing Arduino projects for you to try out someday!
Peter's Arduino Site: Yes, one of the HAGL3 Arduinopunks has a blog for sharing his sketches! Do you? Peter can help you make one!
Taein's Morse Code-SOS.ino: A Morse code ino file by Taein.