@spendius,
Well, I've read bunches, but I don't have Set's memory so I can't just go on and on.
The first book I read that went on about him was formative, as a baseline - not that if I reread it now that I would like the book - maybe I should dig it up from my packed books and reread. It was a good start, whether I would like it now or not.
The Italians, by Luigi Barzini.
http://www.amazon.com/Italians-Luigi-Barzini/dp/0684825007
Of course, my copy was used, old, and crumpled, written many years before this edition shown on Amazon.
I read one book that was pretty detailed about his end days, but of course I don't remember the title. The good news is that I still have virtually all the books I've read about italy, unless they were from the UCLA research library, or police or art procedurals, which are a sort of candy for me, that I tended to save for a while and eventually sold back to used book stores.
I'll nose around and get back to you on books I liked or didn't, re Mussolini. Thinking of a small one, blue cover, early date. Midnight of the gods, or some such inflammatory title.