Grooveshark is awesome, but if you are looking to expand your audio horizons use it in tandem with this -
TuneGlue°
It is a 'relationship explorer'. Basically you tyhpe in some artist you like and it pops out an up-to 11 legged spidergram of other artists they are associated with through collaborations, shared members, etc. Then you can expand each one of them and so on until you have a lattice of connections between loads of artists some you know and love and some you have never heard of.
Pop 'em into Grooveshark and your life gets better.
I've uncovered so much beauty combining these two sites. I'm infatuated with music all over again.
Peace,
kowalski