While searching for links to one of my sites today, I found alexastreet.com and alexadex.com - these are simulated stock markets, based on alexa ranking.

These are great examples of using alexa data in unique and interesting (if somewhat esoteric) ways.

Oh, as of November 13, 2006, alexadex.com is kicking butt on alexastreet.com:

Here's an interactive chart to play with:

alexa website statistics by alexaholic