Here is the label that John Zorn owns: http://www.tzadik.com/
It's about experimental music most of them.

This one is all about doom/death/extreme music http://www.southernlord.com/index2.php (it's the label where Sunn O is on).

And this one is my favourite, all the bands from this one are so so cool: http://www.cuneiformrecords.com/
All progressive music from all the globe.

I hope this will get you to know more cool music

Enjoy!