I'll second:
Boston T. Party (his Gun Bible in particular). Also, be advised that his new novel, Molon Labe, is coming out "in time for Christmas".
Both of Vin Suprynowicz's books.
Victor Davis Hanson, especially Carnage and Cultures, a fascinating assessment of why western civilization has been so militarily dominant for the past 2500 years.
WRT Machiavelli, he was actually a hardline republican. His book The Discourses is more representative of his own views. (The Prince was written to curry favor with a prince who essentially had him under house arrest because he'd been on the wrong (i.e., republican) side in a coup.) A couple of quotes in a review of The Discourses: "The multitude is wiser and more constant than a prince." "A corrupt and disorderly multitude can be spoken to by some worthy person and can easily be brought around to the right way, but a bad prince cannot be spoken to by anyone, and the only remedy for his case is COLD STEEL."
I found Machiavelli on Modern Leadership: Why Machiavelli's Iron Rules Are As Timely and Important Today As Five Centuries Ago by Ledeen to be a quick read and an interesting insight into the man. As always, YMMV.