E-4B up.
One built (s/n 75-0125) and equipped with 52,500-lb CF6-50E2 engines. Has nuclear electromagnetic pulse protection, nuclear and thermal effects shielding, advanced electronics, and a wide variety of communications equipment.
B-52s are popping in now. Have counted 4 up so far.
E-8C Joint STARS
The E-8C Joint Surveillance Target Attack Radar System, or Joint STARS, is an airborne battle management, command and control, intelligence, surveillance and reconnaissance platform. Its primary mission is to provide theater ground and air commanders with ground surveillance to support attack operations and targeting that contributes to the delay, disruption and destruction of enemy forces.
Boeing E-3G Sentry
USAF Block 40/45 modification. Includes hardware and software upgrades to improve communications, computer processing power, threat tracking, and others, and automates some previously manual functions. initial operating capability (IOC) reached in July 2015.
Also spotted interesting Beechcraft 1900D.