That would be Reign of Fire ... here's a link to the official website. It takes place a few years in the future. I'm looking forward to it, but I have a nasty suspicion that the humans will win the war.

caleb68 has a tank and Humvee in Free Stuff.

hasdrubal has an posable M4A3 Sherman tank at The Red Skull's Dungeon.

I'm sad to report that there aren't many posable helicopters flying around. JesterCGI has a nice Bell222 in the Marketplace, with police and camoflauge textures, but that's about it.