Our first entry is by Tim Ltd, who is apparently currently at a university with a limited supply of bricks. He still managed to build this neat little AA gun, which I can envision mounted on a naval vessel of some type.
Next up is a Tunguska tracked AA system by Snuffwuzz >.<, rendered in LDD. Unfortunately, tracks aren't available in the program, so he substituted wheels for them. That doesn't make this model any less impressive, however.
Chris C(from the UK) also has rendered his entries, a ZU-23-2 and a Rapier missile system (both towed AA systems) in LDD.
Carpet Legos has built a FlaK 88, and though he says that this is merely the latest version of a model that he built some time ago, it's highly detailed and is a nice entry nonetheless.
The Legonator turned to microscale for this build challenge and built a very cool AA train, as well as a number of different AA systems.
A relative newcomer to flickr, keegar1 has built a towed SAM system and its accompanying truck.
Tyler TJM's FlySwatter II AA system is built into a tank turret, to act as a defense against aircraft if the tank is without air support. I like the fact that it's concealed, and ready to give a helicopter or low-flying fighter an unpleasant surprise.
Babalas Shipyards has built a pair of Phalanx CIWS on latest work in progress, a massive Royal Navy frigate. They're a dead ringer for the real thing, and, just like the real thing, look like some well-armed version of R2-D2 from Star Wars (as they're sometimes nicknamed in real life).
Like The Legonator, I also turned to microscale for this build challenge, and built a diorama of US forces smashing their way through German lines in
Next up, sniper151516 built an AA version of a Lynx light tank. The photography is a bit grainy, but that doesn't change the fact that it's an excellent and very detailed creation.
And, last, but not least, Aleksander Stein has built the XA-386 Vanguard, and AA version of his XA-380 AMV (Armored Modular Vehicle). Though it's merely a back-up for his main entry, which he wasn't able to finish in time, it's still a definite highlight of the build challenge.