The first one is a site called www.music-map.com It is an excellent website, you type in the name of a band you like and it shows you the artists that are closest related to the band you typed in.
The second, and my favorite, is www.pandora.com You type in the name of a band or group you like and it plays music (like a radio station) from artists that are related to the artist you typed in.
Both are very good sites.
For more general music selection, Shoutcast (www.shoutcast.com) has literally hundreds of Internet radio stations of all genres from around the world.
Well though this is not a free music site, I love cdbaby.com for finding some rather hard to find independant releases. Even a few things I can’t find on free downloading sites. You can also search by genre an state, an I have found some rather awesoem local bands I had never heard of.
On a side note, they also have filmbaby.com an can find some independant movies there.
Independant as in low budget documentries an, horror film an dance;drama, religion, all sorts of categories. I’ve gotten a few just to see an talk about some are way out there.
Archive.org has lots of free Jam band type live recordings.
There is some amazing Derek Trucks, Little Feat, Ryan Adams, Smashing Pumpkins and Phil Lesh and friends, among others there.