Possibly more than you asked for, but it's great material:

http://scratchapixel.com/

(on a not-particularly-raytracing-related note, I can really recommend to anyone interested the lesson about colour spaces, first time the point of CIExy and sRGB became clear to me. also for anyone wondering why the colours in F.lux / Redshift shift the way they do, check the "blackbody radiation" chapter)