Did you miss the mixtapes in the times of mp3 cds?
Here is a cool online version: http://www.mixwit.com/
it combines mp3 searches SeeqPod (http://www.seeqpod.com )and SkreemR http://skreemr.com/) and is really easy to use! after some minutes of copy and pasting songs you could send the link to the virtual tape via E-Mail. Perhaps they will include hype machine and elbo.ws in the future too…
i found the link @ http://blog.go2web20.net/2008/04/music-widget-from-past.html
you should also be able to use it as youtube mixer now..