An interesting programming experiment sought to see whether a game could be stored in a single JavaScript file.  The author chose to implement Super Mario Bros. for the project.  No Flash or Java was used.  While the game isn't coded as completely as the real game (e.g. one level, no power-ups, poor physics, bad music), it is neat to see what can be accomplished in browsers with a small amount of code.  Look at it as a proof of concept of the internet to come.  The author also talks about a few tricks he used, with sprite storage analogous to the way sprites were stored on the NES.  As the game makes use of recent additions to JavaScript/HTML, try upgrading your browser if it doesn't work properly.

Link: nihilogic