You find it at http://build.last.fm/. Awesome!
The following (sociomap) is just one of the many example, most of the others are mashups with video and other information services, and various badges.
Also I’m looking for a web mashups that is able to let me see guitar chords of the songs I watch on youtube or listen on last.fm and possibly automatically tune them based on the tune of the song and possibly automatically scroll them based on the played audio.
Something similar, again from the previous list, is letsplayukulele.com but I play for fun, guitar and not ukulele. Anything similar for guitar chords?