"Genocide Circus", Rebecca and Carol's Combination Attack, where the former surfs on a giant freakin' missile and unleashes all of her ammo before jumping off!
Captain Bartholomew vs. Fereydoon. Even Dean admits that both of them were really cool to watch.
The scene right before where Asgard comes bursting in out of nowhere is pretty epic, too.
Two words: "GET 'IM!!!" Cue Asgard vs. Jotunheim.
Asgard getting his other arm back.
The manner in which the party begins the final battle: The door to Volsung's hall opens, and Volsung looks down the carpeted hall from upon his throne, expecting to see the party walking determinedly towards him. Instead, he sees Dean sitting in the monowheel, and Dean proceeds to rip down the hallway, ducking and weaving in between Volsung's laser defenses while shooting them down, eventually driving the monowheel up a pillar and shooting down the rest of the laser emitters in midair, landing perfectly and driving the final few meters to Volsung - only to get blasted into the air by the last laser emitter, except he doesn't let that stop him, and proceeds to grab the monowheel in midair and force it down towards Volsung (shouting a battle cry that slightly reeks of Narm) - except Volsung finally stands up and blocks the monowheel with his BFS (the S standing for spear), and the screen goes white. When it fades, we find Dean and Volsung, surrounded by flames, and after they slowly stand up, they get into a quick scuffle, moving at the speed of Dragon Ball Z, which finally ends when Dean lands on his feet, the rest of the party runs up, and the final battle begins, after Volsung proving he's a sheer badass with a slick line and the small motion of pushing up his glasses on his nose. Best. Final boss intro. Ever.