mFlow is a very nice and interesting start-up based in Chiswick. They do music streaming on demand, just like Spotify. You can listen it for free. I don't claim to understand their business model (OK, fine, you can buy music there as well, but so you can in zillion other places) but they are extremely nice.
I met with their founder about a year ago and he was super-enthusiastic about this service. Really glad they made it to the beta stage - and really hope they'll keep going with it.
http://beta.mflow.com/signup?invitecode=05N624 - if you sign up using this link, I get 1 pound and can play with paid features of the service :)