The Rider War. Nearly every rider of the last ten years, all their mecha and bikes and special moves in one climactic Final Battle. And this is THE VERY FIRST SCENE.
Later on in Hibiki's World, when Decade, Diend, the original Ibuki and Zanki, and their successors team up in a united performance to defeat a giant monster. Might qualify as Crowning Music of Awesome as well, not to mention a stellar example of The Power of Rock.
Also from the movie: Diend summons Kamen Rider J. Then he turns Decade into a giant Decadriver, which mounts on J's waist, turning him into a titanic Decade Complete Form. The other Riders leap into the air, turning into KamenRide cards of themselves. Jumbo Decade leaps through them, performing a Rider Kick as large as J's own giant kick, but with more explosive power.
Let's just say that from the second you hear the VROOM!! of the bikes of Riders 1, 2 and V3 in their and almost all other main Riders' Big Damn Heroes moment, everything just becomes a crowning fight scene of awesome.
The entire last twenty minutes of All Riders vs. Dai-Shocker, starting from the "VROOOOM!" and only getting awesomer from there.
Yusuke's transformation into Ultimate Kuuga from Episode 2 and the subsequent fistfight he has with Decade. The Supreme Warrior vs. The Destroyer of Worlds, it gave me goosebumps.