The Arduino Challenge on Instructable is currently open for entries of all projects Arduino-related.
Also, don't forget to enter your Arduino project into the Make it Real Challenge. You can win one of many 3D printers, including an Objet Desktop UV-curing printer! To be eligible, your project simply needs to contain an element that was designed on a computer (a schematic, or even a sticker will do!).
If you enter your project into both contests, post a link to it below, and we will make you a free 3D print of any model you want within a 3" x 3" x 3" bounds.
I know last time we ran an Arduino contest, there was a little bit of disappointment that it was only open to citizens of the US and Canada. Our contests are now open to citizens of the US, Canada, the UK, Australia, the Netherlands, Belgium, and China.
If your country is not on that list, please let us know! We will work hard with our legal team to get it added.