Here are some of the graphics people I follow on Twitter and whom I personally consider experts in the field:

Fabian Giesen: https://twtter.com/rygorous http://fgiesen.wordpress.com/ -- RAD Game Tools

Sean Barrett: https://twitter.com/nothings -- ex-Looking Glass, now RAD Game Tools

Brian Hook: https://twitter.com/GrumpyHook -- ex-id Software, now RAD Game Tools

Romain Guy: https://twitter.com/romainguy -- Google (Android)

John Carmack: https://twitter.com/ID_AA_Carmack -- id Software Founder / Occulus VR CTO

Johan Andersson: https://twitter.com/repi -- Technical Director on Frostbite Engine at DICE (Battlefield Games)

Dave Moore: https://twitter.com/dmmfix -- RAD Game Tools

Tom Forsyth: https://twitter.com/tom_forsyth -- ex-Valve (?), ex-Intel, now at Occulus

Graham Sellers: https://twitter.com/grahamsellers -- AMD

Matthäus G. Chajdas: https://twitter.com/NIV_Anteru

Christophe Riccio: https://twitter.com/g_truc -- ex-Imagination Technologies, ex-AMD ?, now indie?

Robert Menzel: https://twitter.com/renderpipeline

Morgan McGuire: https://twitter.com/CasualEffects