Physically Based Shading in Theory and Practice

http://blog.selfshadow.com/publications/s2014-shading-course...

http://blog.selfshadow.com/publications/s2013-shading-course...

http://blog.selfshadow.com/publications/s2012-shading-course...

http://advances.realtimerendering.com/s2011/index.html (not sure there was one in 2011...)

http://renderwonk.com/publications/s2010-shading-course/

This is a good, high-level intro:

https://www.marmoset.co/toolbag/learn/pbr-theory

https://www.marmoset.co/toolbag/learn/pbr-practice

This page has links to more than you ever want to read:

https://interplayoflight.wordpress.com/2013/12/30/readings-o...

http://dl.acm.org/citation.cfm?id=2776880&picked=prox&CFID=7...

But in some cases, the pdf files from the ACM just provide links to other sites (like the submitted link to selfshadow.com).