I am invisible, understand, simply because people refuse to see me.
--Ralph Ellison
I would read them in the order they came out:
The Fall of Reach
The Flood
First Strike
Ghosts of Onyx
Contact Harvest
Cole Protocol
Evolutions (I & II)
Cryptum
Then read the terminals from Halo 3.
Other sources of canon: The graphic novels, Legends, Dr. Halsey's journal, data pads from Reach
Coming soon: Glasslands, Primordium and CEA terminals
[Edited on 08.03.2011 5:48 PM PDT]