I have just finished writing Pong, my first full featured game, in Rubygame.
On top of just the normal Pong action, I have added sound effects and background music.
I have uploaded my source code to my website. Consider the source code "free", i.e. do what you like with it.
You can browse the source code online.
Giving credit where credit is due:
The main tutorial I used to learn how to create Pong was from the "Rubygame Book". It is an excellent starting tutorial. It explains a lot of the initial framework setup.
The background music is from the Rubygame samples. These can be found with the latest release of Rubygame.
The sound effects are from http://freesoundfiles.tintagel.net/Audio/
Feel free to ask any questions you may have regarding the source code, or other ruby related issues you may have.