The Sixtyone is my favourite music site. Its free for both audience and artist. Its easy to use because its community of users does the work for you. All you have to do to get into it, is press play. You'll discover some new music you like. A couple of artists I have the pleasure of working with have put some stuff up on there - check out Freddie Stevenson and Barry Adamson.
Its not a massive site yet. According to the61 blog the most listeners its had at any one time is around 10K. So there is a bias towards a particular genre - from what I can tell folk and singer/songwriter stuff seems well represented. That's cool with me 'cos I like it - and Freddie seems to be reaping the rewards judging by some of the comments to his tracks. However, I have seen comments that some genres - metal for example - aren't properly appreciated on the61. That may be true - but bear in mind its early days, and I was still able to hear for the first time this awesome guitar hero style instrumental rock track from Buckethead - for the moment its still set as one of my 'profile tunes'.
So that's a brief introduction to the61. My profile is here. I'll expect writing more about the61 as I get the time to do so. I think the combination of a game play structure and a community energises the site through the increased activity rates of its users (I don't think I've been as active - as a user - on any other site - except perhaps google but that's not the same thing). For me it shares something with Habbo (the great untold success story of the internet) by the way it mixes competitive and co-operative dynamics in a new and interesting way. Genres are perhaps the one area that I'm not enamoured with, but I'll save my thoughts on that for another day.
In the meantime, big thanks to the two young guys who created the site from their dorm room - James and AN Other.