I'm an aviation buff, so excuse the lack of ground vehicle representation in the list below:
Number one coolest thing: A brochure for an all-new missile by Raytheon called the Advanced Extended Range Attack Missile (AERAM) for cruise missile defense. I'll upload the brochure as soon as I can get to a scanner, but it shows a picture of something that looks vaguely like Raytheon's Miniature Air-Launched Decoy. According to the brochure, it's intended to attack cruise missiles, unmanned air vehicles "and other symmetrical or asymmetrical airborne threats bearing conventional weapons or weapons of mass destruction that present a current threat to the US homeland and US military.
Number two coolest thing: the Lockheed Martin P44 missile concept. I don't know much about this weapon yet, but, juding from the mock-up at the booth, I'm guessing it's Lockheed's answer to Raytheon's Precision Attack Missile (PAM), but with elements of Lockheed's much-postponed Loitering Attack Missile thrown in. So, think PAM with longer range.
Number three coolest thing: Sikorsky's poster showing a picture of the X-2 high-speed coaxial-rotor helicopter as a gunship. The US Marine Corps someday will likely need an armed escort for the 270kt V-22 tiltrotor, and I'm guessing this could be one of the candidates. The X-2's first flight is in December, so watch this space for updates.