Well, your first port of call should be the Raven Guard Index Astartes. See here
for the part that is relevant for Pre-Heresy. There is a discussion here
about what marks of armour the Legion would have had available in the Pre-heresy/heresy period that may also prove helpful. Corax himself makes appearences in the Heresy novels - he features in Fulgrim
, The First Heretic
, and is also the main character in the Raven's Flight
audiobook, and the Legion is guaranteed to be the main protagonists of the upcoming Deliverence Lost
which will doubtless shed more light on the Legion as a whole. In addition, Imperial Armour 8 has a section on the Raven Guard, although it largely repeats the information given in the Index Astartes article.
Hope that provides you with enough to get started! This post has been edited by The Red Sorcerer on Jul 26 2011, 10:21 AM