Back in 2006 Lee Byron produced a stream graph of his listening history.
Inspired by Lee's work, Andrew Godwin produced LastGraph, a tool that allows you to generate a Last.fm listening history graph for any user. Here's mine.
And my listening frequency.
A Flickr group has been set up to host LastGraph charts (and many other Last.fm visualizations):
In February 2010, Frederik Seiffert released LastHistory for the Mac as part of his diploma at the University of Munich. You can browse any Last.fm user's listening history via a timeline scatter plot. You can also correlate your own listening history with events in iCal and pictures in iPhoto as demonstrated in the video and image below.
Recently, Martin Dittus produced Heatmap Calendars of selected Last.fm users' scrobbling activity. The calendars allow you to see various patterns representative of different listening behaviours.
There are many other visualizations of Last.fm data, for example its social networks and charts, but I'll save those for another post.