Spencer Ackerman notes that there are plenty of non-Republicans well-qualified to serve as Secretary of Defense:
Jim Webb. Richard Danzig. Michele Flournoy. John Hamre. My personal favorite — though apparently not eligible to be secretary until 2010 — Tony Zinni. (Who probably isn’t actually a Democrat, but is also not a Republican, and whom the building would greet with sweets and flowers.) Ash Carter.
Right-o. Two other ideas -- Lee Hamilton, Larry Korb.