youtube but be careful! i listen to metal, and there are some really really dark corners of youtube where no user should ever go... good luck my friend
Check out who your favorite artists collaborate with. Go back to your favorite albums and see who produced it (if you haven't already).
I look for it. But seriously, what I do usually is I find an artist that I like the sound of then I look at the record label that signed them and see who else they've signed
Usually through friends. People telling me to look up different artists/songs. Other than that, I usually just stumble across good songs through skate videos and such.
Friends Last.fm Turntable.fm Surprised no one has said turntable yet, it's one of the coolest music websites out there.
Youtube Pandora Music Hall on GC Friends Sometimes the radio I use the app SoundHound on my phone a lot too. You just press listen while a song is playing and after like 10 seconds it comes up with the artist and stuff.
I ask everyone I know what music they like...its the best way to find music...I used to burn mixes for people and then they would do the same in return....music sharing is fun....I mean its cool to have Pandora or last.fm or spotify sometimes but there's nothing like listening to new artists with someone else