The Gathering

Have just had a try at Spotify ( http://www.spotify.com/en/ )
This allows you to play music on your PC or Mac without needing to purchase it or downloading it to keep permanently. You have to register, and install a small client program on you machine.
I have only had a very quick look at the range of traditional music available, but so far have been quite impressed.

Showed Spotify to my son a short while ago and he said "Have you tried Last.fm?"
This provides a similar kind of service, but generates a virtual radio station, based on, but not restricted to, any artist whose name you type it, and plays effectively for ever until you stop it. So unlike Spotify what you get is not completely predictable, and may contain surprises. (I am currently listening to "Phil Cunningham Radio".)
The web site is at http://www.last.fm/