I got this one from Paul Lamere’s MusicMachinery blog…. it’s so cool. Not really super useful yet in my experience, but TOTALLY COOL even so.
You install LastHistory. You put in your Last.fm username. It parses through your listening history. Then you get a graphical representation of your listening over time, that looks something like this.
But you won’t get it, quite, til you play with it yourself. To save you time in doing so, I recorded a ScreenJelly screencast so you can see the interaction. Unfortunately ScreenJelly seems not to embrace remote embedding so you’lll have to make the jump to their domain to see it…. here it is. 
http://screenjel.ly/watch/OAi7kRm2o4o