Books:
o Sam-Ang Sam: “Silent temples, songful hearts: Traditional music of Cambodia"
More Information + Order: Here  

o Amy Catlin, Eran Fraenkel: “Selected Reports in Ethnomusicology: Text, Context, and Performance in Cambodia, Laos, and Vietnam"
More Information + Order: Here

CDs:
The number of audio CDs dealing with “traditional” music is huge, this is why I only like to recommend CDs that I know.

o Various Artists:  “The Music of Cambodia“ (Box Set) 
More Information + Order: Here

o Chum Ngek:  “Homrong“ (overtoure music)
More Information + Order: Here

Please also check the Musicians page, most of them publish books and CDs too!