writes "MAKE Magazine has put together their 3rd annual 'State of Open Source Hardware 2008' — in just a few years, the number of projects has grown from a small handful to an amazing 60+ offerings. Similar to open source software, open source hardware is available with source code, schematics, firmware and bills of materials, and allows commercial use. The most popular project, Arduino, the open source prototyping platform for artists and engineers, has shipped over 60,000 units."
The article is formatted such that the first link for a particular device will usually take you to the project home page. Some will bring you instead to where you can purchase the items, but most still have a "How To" tab which will direct you to guides and instructions on how to build your own gadgets. There are a bunch of interesting devices, from the Game of Life on the outside of a cube
to a home-made MP3 player