For the last year my work tunes have been provided by pandora. I had a couple stations that I had pruned and edited to my liking - to the point that I was seriously considering subscribing. I didn't mind the unobtrusive ads and the 40 hour a month limit just reminded how much I relied on it and inspired me to drop some cash their way. 

 Before I got a chance to do so, however, they switched up their ads to annoying audio ads that seem to show up every couple songs. The ads seemed to be louder than the music I was playing too. Around that time someone suggested I look at grooveshark. I had tried it before but their strange UI had turned me off. It seemed to confusing to bother with. Apparently enough people thought so that they put some good work into the ui, making it much easier to parse and understand what you were doing. Grooveshark seems to have the best mix of features compared to pandora, last.fm and lala.