click the link below for the mp3. It's most likely legal because it's hosted on Sigur Rós's official site.
http://download.sigur-ros.co.uk/sigur_ros_untitled8.mp3 (http://download.sigur-ros.co.uk/sigur_ros_untitled8.mp3)
Even if you don't like slow stuff, just listen to the entire song, trust me on this.
It's an amazing trip of a song, really...
also, if you were wondering, the vocals are sung in Vonlenska, which is the nonsense "language" the band made for a lot of their songs. It's absolute gibberish :)