If you havent heard of it yet, check out Grooveshark.com.
Ive been using this website to stream music while at work and really enjoy it. Similar to Pandora but doesnt have rules about changing songs and whatnot, and instead of channels, you creats your own playlists . boasts to have 7 million songs ATM. All free, ads arent annoying at all, and a very easy to use interface. Widgets for your blogs, and soon to be mobile for yer smartphones. which is really cool!

I am actually doing a promo party in Miami to kick off there mobile service at the end of the summer. But i definitely think it is a great way to listen to whatever you want to online, without using Youtube and Pandora.