EMP mines, set by GDI Riot Troopers. These mines disable enemy vehicles and cyborgs.
Barracks: See enemy infantry roster
War Factory: See enemy vehicle count
Refinery: See total enemy credits
Power Plant: Disable power, most noticeably the Tesla Coil if present
I forget if infiltrating the Construction Yard or Radar Dome did something; I want to say disable passive base repairs and reveal enemy positions respectively, although I could be wrong.