My son Jake turned me on to pandora.com.  You create an internet radio station based on artist, genre, or song and they find similar music for you to listen to.  I've even created a Mojo Rib station

Yes. I've used it alot at my office where I don't have a sound system or radio. (Also did a Rib station!)
link

I use it and love it.

I wish I could use it in the office, but our system administrator blocks it, uses too much bandwidth.

Pandora rocks!

(or blueses, jazzes, countriesessess, etc...)

Use it all the time when I am actually home, which unfortunately isn't much nowadays.

Check out http://www.seeqpod.com It's a search engine for mp3's, wma and videos (including youtube). Allows you to create a playlist and then plays them in whatever order you select. Downside vs. Pandora is that you have to do the work with the song selection and you didn't try new artists (big + for Pandora for me), but the flip side is that you get to hear crazy, rare stuff like Pearl Jam and Neil Young playing "Rocking in the Free World" and then watch them destroy everything on stage :-D

BTW - link is http://www.youtube.com/watch?v=PTTsyk-pyd8 for that vid

It's way better than Yahoo radio, which doesn't really pay attention to your preferences unless you buy the premium package. No matter how focused I made it on classic rock, I would still get newer pop songs thrown in every once in a while, which I hate.