Nusic.fm has all of the features you would expect given the title of this post, as well as a stack that allows you to play tracks from Youtube and Soundcloud (more services coming soon) whilst still browsing the site for other content. The cool thing about this is that to the user it appears platform agnostic - using the stack with any media source seems exactly the same. No more following links to different sites to play media and comment on things, it all happens on one site, seamlessly.
The site also allows 'combined charts' (think merged subreddits), so if you are interested in 2 (or more) genres you can make a personalised chart showing both at once, with ease.
Naturally, we have last.fm scrobbling integration and lots of other nice little features, thanks for taking the time to read this and we hope you like the service! Feedback (good or bad) would be greatly appreciated.
Sam and India (Nusic.fm, UK)