Acclaimed historian David McCullough (author of such terrific books as 1776; Truman; The Great Bridge: The Epic Story of the Building of the Brooklyn Bridge; Mornings on Horseback; John Adams; The Johnstown Flood; and The Path between the Seas: The Creation of the Panama Canal, 1870-1914) also wrote an introduction to the 1992 classic study by Charlton Ogburn, The Mysterious William Shakespeare.
Among his recommendations of the book, McCullough wrote: "The strange, difficult, contradictory man who emerges as the real Shakespeare, Edward de Vere, the 17th Earl of Oxford, is not just plausible but fascinating and wholly believable. It is hard to imagine anyone who reads the book with an open mind ever seeing Shakespeare or his works in the same way again"
I'm glad I bought my copy of Ogburn's book when it first appeared because it is getting a bit pricey to purchase nowadays. However, you can save your dough and still get a good introduction to the key issues of the Authorship Question by reading this enlightening interview of Charlton Ogburn conducted by Dr. Sheila Tombe for Apostrophe back in 1996.
You might also enjoy checking out a couple of other Book Den posts which relate to the "real Shakespeare." They are here, here, over here, and finally right here.