Here is a cassette tape case, printable without support structures. I recommend printing parts 1 and 2 in one color and part 3 in another color. I went through 6 iterations to get it just right.
For assembly guidance, watch this video: http://youtu.be/96-FlXv9jAY
You can customize this with album art using SketchUp. Also check out this version with logo templates: http://www.thingiverse.com/thing:652692
Please list this file as the source on all remixes/customizations and follow the rules of Creative Commons - Attribution - Share Alike.
Before attempting to print this, make sure your printer is well calibrated. The parts are designed to fit snugly. I recommend this calibration tool: http://www.thingiverse.com/thing:342198/#instructions
Big thanks and credit to my friend Austin Gaines for coming up with the idea.