mplayer should work. I went to last.fm, and saw that it's flash. So, I tried it and I got it working. I've got flashplayer 10 installed (specifically, from the package flashplugin-nonfree). Installing mozilla-mplayer and sun-java6-jre is a good idea, too (though likely not necessary for these sites).
If you already have flashplugin-nonfree, perhaps you could try "sudo dpkg-reconfigure flashplugin-nonfree", which, I think, will update flash to the latest (I say this assuming that Ubuntu has a flashplugin-nonfree package -- I use Debian, so I figure Ubuntu has got something similar)
Last edited by mark_alfred; 07-06-2009 at 12:33 AM.
Reason: Made an incorrect assumption about streaming media