Grooveshark is one of my favorite music sites, and I just signed up for a year subscription to Grooveshark Anywhere (normally $3/month or $30/year) and that allows me to listen all the Grooveshark music I want, advertisement free, and it lets me scrobble that music to Last.fm (which is the main reason I upgraded to the subscription!) and if I owned an Android phone I could also listen to Grooveshark on my phone. I love using Grooveshark because there are an unlimited number of songs and artists that I can choose from, any song I have looked for, I have found it on this website! And it's completely free (and legal!) to listen to all the songs!
Last.fm is also one of my favorite sites, it keeps track of what music you listen to (on computer, ipod, etc) and charts it for you.. top tracks.. top artists.. check out my last.fm profile. Now my last.fm scrobbles won't be limited to just the songs I own and have on the computer! YAY!