I second live365. You'll find just about anything you're looking for there, and the quality is quite good, for the most part.
If you want ad-free though, you'll have to join as a preferred member - about 3-4 bucks a month, depending on how (often) you want to pay.
want to add another one: www.klassikradio.de
The website of this german radio station offers livestream.
Together with "normal" classical music, opera and contemp. classical
music they also play soundtracks - at least two ore three pieces
per hour. It's my favorite radio station so far.
Check it out.