Hello, I am a Literature Faculty student in Edirne, Turkey. I have long searched for translated sources concerning Pre-Islamic Turkic History. Although we have a good many books in Turkish, there aren't any reliable ones that I could find on the internet.

Since the Turkic Peoples were mostly nomadic, only some inscriptions and memorials could be found and interpreted. And for books, there are many Chinese sources. So these are the main sources we have studied:

Orkhon Inscriptions:

http://en.wikipedia.org/wiki/Orkhon_inscriptions

The Orkhon Inscriptions: Being a Translation of Professor Vilhelm Thomsen's Final Danish Rendering

Kul Tigin:

http://en.wikipedia.org/wiki/Kul_Tigin

The Kultegin Inscription (1-40 lines)

Tonyukuk’s Memorial Complex

The Bilge Kagan Inscription

And in this site you may find various Turkic information.

Sources:

Language Committee of Ministry of Culture and Infrmation of RK

Bulletin of the School of Oriental Studies, University of London, Vol. 5, No. 4 (1930), pp. 861-876

Ahmet Taşağıl-Göktürkler,cilt-1,Atatürk Kültür, Dil, ve Tarih Yüksek Kurumu Basımevi, 1995

Muharrem Ergin, Orhun Abideleri, 7nci baskı, Boğaziçi Yayınları, 1978

If you are interested in the turkic peoples and central eurasia in general there is Empires of he Silk Road by Christopher Beckwith who is a professor at Indiana University. Might be a bit grander in scope than just that one specific empire but I know there is plenty devoted to them as well as decendents and whatnot.

The author claims he wrote the book siting a general lack of literature about centeral Eurasian peoples along with many miscoceptions about the culture of such peoples.

I just picked it up and its my first brush with the subject so I can't give a formal reccomendation so if anyone else is familiar with the work and can comment on it I'd appreciate it!