There are a lot of free radio channels available on the Internet. I listen to NPR frequently and I have the choice of listening to stories directly on the main site www.npr.org or I can listen to programs on just about any member station -- most of them have direct broadcast feeds I can access with 2 clicks of my mouse.
Pandora Radio is different than a simple all-music station. This one is called the Music Genome Project (tm). The concept is that if you input a song or an artist (called a seed) the software will queue up additional music that it thinks you will like, based on your input. As the tunes are played, you can rate them (thumbs up, thumbs down) and adjustments will be made to your next song. There are pre-selected Pandora "stations" seeded with just about every genre of music you can think of (although they only added Classical Music this month).
While it's sort of cute that the company uses a tag such as the Music Genome Project, calling songs or artists "seeds" instead of "genes" means they haven't taken the metaphor to the extreme, though I'm guessing they were tempted. And with the name Pandora (all gifts) it was inevitable that I blogged about the service -- myth AND genome. They're as crazy as I am.
You will see ads on the webpage as you listen and they occasionally change as new music is queued up. They also sell small units that allow you to listen to Pandora as if from an AM/FM radio. But I don't find the ad intrusive -- I open a separate browser tab, open my Pandora account, and leave it alone. My tastes are very eclectic, some of my "stations" are:
Keltoi and Medieval
Symphonic, Romantic period
Dead Can Dance Radio
Acid Blues Radio
Give it a try. It's free.