I'm also a fan of Pandora, and Radio paradise. Radiotime.com is an aggregator of streaming stations used by several music servers (including Sonos, Autonomic Controls, and Nuvo) which can also be accessed from any PC.
Spotify allows you to listen to any song, at any time, if it's in their catalog. Free version is commercial supported, and $10/mo is commercial free. When I tried the paid version a year or so ago, I found their catalog lacking, but tried it again recently and was surprised to find more selections.
I'd like to plug WTMD, a public radio station (no commercials) out of Towson, MD. 'Radio for Music People,' they offer quite a mix of cutting edge indie, classic rock (think Steely Dan), and some 50s and 60s. Streaming online at WTMD.org. Similar mix to Radioparadise.