Different people interpreted the question in different ways. Some folks wrote about the historic sources they study most often, such as the Cornwallis Papers, Peter Force’s American Archives, the Papers of George Washington, or more specific collections. In my case that might include the Boston Town Records published a century ago.
Others spotlighted one-volume histories of the war: John Ferling’s Almost A Miracle, Merrill Jensen’s The Founding of a Nation, Robert Middlekauff’s The Glorious Cause, and The Spirit of Seventy-Six: The Story of the American Revolution as Told by the Participants, edited by Henry Steele Commager and Richard B. Morris.
Yet others named their favorite reference volumes: Mark M. Boatner’s Encyclopedia of the American Revolution, Richard Ryerson and Gregory Fremont-Barnes’s Encyclopedia of the American Revolutionary War, and The Blackwell Encyclopedia of the American Revolution. For researching officers on the two sides, there are British Army Officers: Who Served in the American Revolution, 1775-1783 by Steven M. Baule and Stephen Gilbert and the venerable Historical Register of Officers of the Continental Army During the American Revolution by Francis B. Heitman.
I interpreted the question that last way, but I realized that these days I usually don’t refer to any reference volume at all—I use Wikipedia to get the basics and then do my first followup through Google. Need to know the difference between Charles Lee the general and Charles Lee the Attorney-General? It’s just a few clicks and a little disambiguation away. I was pleased to see that a few of the folks commenting on the posting admitted to that same approach.
But I keep reading books as well, and over the next few days I’ll talk about some from the past year.