I love Pandora so much that I've paid for the premium version of their service. It's a fantastic website. I usually have it open in another tab whenever I'm on my laptop.
Since I switched sides of the office, I use Pandora regularly. Speakers carefully placed, and volume kept low enough the customers at the counter can't hear it.
I used to run an internet radio station, and was a presenter on FM for about a year. It was the most fun thing I've ever done. I've never heard an internet radio station I like ( other than my own; that was perfect ).
It's changed a lot since I last used it, but I used to use last.fm a couple of years ago to listen to classical music while web surfing. Discovered a lot of new ensembles from there.
Pandora is by far my favorite as far as internet radio goes. I've discovered some great music thanks to it.