Why in holiness heckdom is Grooveshark not considered as one of the better alternatives to Last.fm or Imeem? For me it's better than both! It's so good, it's almost like having an entire album for free! And no, it doesn't have that 30 second limit that Imeem has (which I found quite ridiculous as some of the better parts of most songs don't just last 30 seconds) nor does it require you to create a "radio" that basically plays other artists that you don't want there in the first place like Last.fm's.
Here's a sample of a song off of my faves:
Definitely a great site to listen to while surfing the net for blog stories and while writing posts.