3Voor12 has a *HUGE* archive of streaming concerts available on their site... very generous. They could use an easier to use archive -- their flash-driven archive isn't a complete list -- but their site's search features more than make up for it, as they let you listen to (and occasionally view) not only concerts, but individual songs in their deejay's playlists. (The Beeb should do this!)
Just listened to a Lamb concert... now listening to Sigur Ros... and you can even find "Lute Score" by
imomus. A wealth of new sounds to hear and media you can get blissfully lost in... and they have rss feeds so you can track it all, such as 
3voor12concerts, which lists the latest concerts they added to their archive. 