What, no Gainax yet?
Final episode of Tengen Toppa Gurren Lagann, the Gunbuster massacre, Buster Machine No. 7 completely DESTROYING Titan, one of Saturn's moons, the first RE: Cutie Honey OVA with Natsuko VS a horde of Panther Claw lackeys with only one gun on her, all highly entertaining (third one isn't that appetizing, though, considering we have to see a bunch of Topless ripped to pieces by the fluctuating gravity well) and well-animated, though Gunbuster was done in the 80's.
As for the best, though...
http://www.youtube.com/watch?v=zixtPX-W6SY is definitely the best I've seen. Sure, the animation isn't that great, but that's because they were rushed and couldn't finish in time, resulting in what could be called a preview of what's to come. Considering the screencaps I've seen of the DVD version, they made the best fixes possible, turning something with great animation but poor art into a fight so pretty I could cry, and I probably will.