The entire first half of episode 1, when the idols put on their performance while being attacked by military tanks and riot forces. Especially if the viewer was expecting a normal slice-of-life show, and then got an amazing futuristic action sequence instead.
The WOTA brigade who enter in episode 6, deploying a handheld glowstick missile barrage and mecha decorated with AKB0048 members to assist Team 00 in fighting off DES.
Episode 9: Coordinated Multiple Concerts as a decoy for the main event.
Episode 13 in its entirety. No, seriously. The awesome is so widespread in the episode there is no way to pick and choose among it.
Episode 21:
Yuuko defending Akibastar and becoming Center Nova in , even considering how she Disappears into Light at the end.
Mikako showing why she's the best pilot in 0048's history.