I want to share with you what i have found some days ago. Actuallyi was looking for topic to write an essay and i saw an amazing infographic. There are some playlists for each type of writing and you can follow links to grooveshark. I've done my essay and i guess its pretty good as i listened to music. Havent tried it before! See if you like
http://visual.ly/what-best-music-your-h ... nt-writing