My guesses ...
- Huckabee (McCain) or Thompson (Romney) for VP
- Giuliani may be picked for Homeland security (most likely by McCain).
- Gen. Petraeus for Secretary of Defense (McCain and Romney)
H
Gen. Petraeus is not eligible to be SecDef as there’s a 10-year minimum gap required between military service and appointment as SecDef:
10 USC Sect. 113 says:
(a) There is a Secretary of Defense, who is the head of the Department of Defense, appointed from civilian life by the President, by and with the advice and consent of the Senate. A person may not be appointed as Secretary of Defense within 10 years after relief from active duty as a commissioned officer of a regular component of an armed force.