Partially because of the influence of Eric Wagner's Schroedinger's Cat class and partially through an existing inclination, I've been immersing myself in Beethoven lately. I've just started the second revised edition of Maynard Solomon's Beethoven. I also plan to read the Beethoven book that Roman Tsivkin recommended to me, Beethoven: His Spiritual Development by J.W.N. Sullivan (available free here) and to read the book that Eric suggested for me, The Beethoven Quartets by Joseph Kerman.
I've just started the Solomon, but the "Introduction to the Revised Edition" has a paragraph that mentions several topics that Solomon believes merit further research. It includes this: "It also seems to me that it may be time to take stock of the threads that connect Beethoven directly or indirectly to Freemasonry; there is now sufficient evidence to hypothesize that Beethoven remained influenced by Illuminist and esoteric trends in Freemasonry after his departure from Bonn, even though there is no indication that he actually belonged to a Masonic lodge."
In related news, the Bach Guild's new Big Beethoven Box is available for 99 cents from Amazon. It's a nice mixture of the familiar and the less familiar. I bought it yesterday but I haven't had time to listen to it yet.