In case you didn't know, I've been working on an AVR based synthesizer. You can check out some of the videos that show it off here, here, and here. Since then I've been working on getting the source code, schematics, and documentation together so that you can build your own. Now with the new GitHub setup, I've published all of the files, schematics and documentation. Please read the ReadMe as there is some important stuff in there and I'm always happy to take questions if something in what I've published doesn't make sense. Check it out.
On a related note, I'm putting in some more work on this to enter it into a project on Instructables. I'm going to enter it into 2 categories: the musical instruments and Arduino contests. If you belong to Instructables and like my project, go ahead and give it a vote. If I do win, I will be returning the favor to my audience with a few giveaways. I'll post again when I have the entry ready with a link.