First of all, thanks for the sticky Mr. Dave.
Here is a list of some of the free books available on the net which should be present in the collection of each and every graphic programmer.
Free Game Programming ebooks ( general and Opengl related)
The openGL red book
http://www.opengl.org/documentation/red_book/
OpenGL programming guide
http://fly.srk.fer.hr/~unreal/theredbook/
Michael Abrash's Graphics Programming Black Book
http://public.planetmirror.com/pub/gpbb/
Waiting for the feedback of all you ppl.
Hope it helped.
Yours friend,
~s.o.s~