Books:
o Amy Catlin, Eran Fraenkel:  “Selected Reports in Ethnomusicology: Text, Context, and Performance in Cambodia, Laos, and Vietnam”
More Information + Order: Here
o Phong Nguyen:     “From Rice Paddies and Temple Yards: Traditional Music of Viet Nam” (Bk&CD ed)
More Information + Order: Here
o Pham Duy:   “Musics of Vietnam” (Southern Illinois University centennial publications)
More Information + Order: Here
o Phong Nguyen:   “Father Mountain & Mother Sea: Living Musical Traditions of Vietnam”  (Performance in world music series)
More Information + Order: Here
o Tuan Hung Le:   “The dynamics of change in Hue and Tai Tu music of Vietnam between 1890 and 1920“ (Working papers)  
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.
If you like to get an overview of CDs on the market you can check an Amazon-research here.

o Tran Van Khe:   “Improvisations“ (Mostly very beautiful instrumental tracks)  
More Information + Order: Here
o Tran Quang Hai:   “Vietnamese Zither“ (Beautiful solo pieces for the Tranh)  
More Information + Order: Here
o Phong Nguyen:   “Song of the Banyan“ (A nice CD with different ensemble music)  
More Information + Order: Here