This is my new favourite site of the moment:
Last.fm - The Social Music Revolution
I'm only browsing at the moment, but it is possible to sign up (free) for a radio station similiar to Pandora. A plugin can also be installed which will upload a list of the tracks that you play on iTunes or whatever - this information is used to build 'popularity' charts.
I use the site to find similar bands to those I like and then I can listen to the most regularly played songs for that band and then if I like them I will put a poster up on my bedroom wall and maybe get a tattoo.
I also listen to BBC Radio 6 - a fine, fine radio station.
BBC - 6 Music - Homepage