Then I hit upon using one as an MP3 player. Surprisingly, no-one has completed one yet as an 'ible so I decided to go down this path. The hardest part was trying to find the right MP3 to be able to mod. I finally found this MP3 Player on Ebay which fits really well into a cassette tape once the insides are removed.
The only changes you'll have to do is a bit of trimming to the cassette tape with a dremmel, a little bit of soldering and some design work and your done.
So in the name of irony, I present to you this Cassette Tape MP3 Player.
Step 1: Things to Gather.
1. Cassette Tape (get a few of these if you can, I found mine at a second hand shop, about the only place you can get them now. Make sure it uses screws to hold the case together.
2. Labels - These are used to add your own images to the cassette tape
3. MP3 player. Can be found on EBay.
4. 4 momentary push buttons. These you will pull apart and use as replacement switches.
5. Thin black plastic. i.e. from a oil container
4. Stanley knife
5. Hot glue gun
6. Sharp scissors~