Sixth World Wiki is a great place to start. After that I really like the recent Corporate Guide, it gives a good rundown on the history of the various corporations and their shenanigans, which I personally love.
I haven't read a lot of Shadowrun fiction, I'm actually planning on getting back into it a bit, but Dance with Dragons is keeping me momentarily distracted.
I did however read the very old "Never Deal with a Dragon", which I remember being pretty cool.