As Ineski mentioned, the David Ben biography will be a major help, as well as the books contained in the Essential collection, but here are a few other resources you could look at:
The Magician and the Cardsharp - Karl Johnson - the story of Dai Vernon's search for Allen Kennedy and his centre deal
Phantoms at the Card Table - David Britland & Gazzo - mainly about Walter Scott, but with some good material to give texture about the New York magic inner circle in Vernon's heyday
Revelation/Revelations - SW Erdnase & Dai Vernon - Dai Vernon's annotations on Erdnase, also containing some personal reminiscences from Persi Diaconis in the introduction
Revelations (DVD set) - Dai Vernon sessions, reminisces and generally holds court with Gary Oulette, Michael Ammar and Steve Freeman
Greater Magic - John Northern Hilliard - useful as a comprehensive overview of all branches of magic in the 1930s when Vernon was making his name, including some material contributed by Vernon himself as one of the "Card Stars of the USA"
Expert Card Technique - Jean Hugard & Frederick Braue - famously contains many Vernon techniques uncredited, hence his special additional chapter in the third edition, which is also a useful insight into his thinking
Stars of Magic - George Starke - contains many of Vernon's well known effects, and those of his contemporaries who were developing the art of close-up magic
The Vernon Chronicles Volumes 1-4 - Bruce Cervon - contain lesser known effects and sleights from Vernon and his circle, plus historical notes, especially in Volume 4 which is effectively a Vernon biography
The Vernon Touch - a compilation of Vernon's columns in Genii magazine
Early Vernon - Dai Vernon & Faucett Ross - Vernon's original $20 manuscript, with additional material and history
In addition, to understand the development of close-up magic in parallel with Vernon's life, it would be useful to have read the early Hugard books, especially the Card Manipulations/More Card Manipulations series, and Close-Up Magic (originally Close-Up Magic for the Night-Club Magician. And, of course, to understand Vernon, Erdnase is essential.
Hope this is useful.