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.
Note the use of "Diend Form" after the monster's name. Chinomanako had stolen the Diendriver from Kaito, and became the Big Bad of the arc due to his very existence as an Ayakashi Rider causing the Shinkenger world to unmake itself.
In Black RX's arc, Tsukasa obtains Apollo Geist's Perfector, which he uses to absorb the life energies of people so that he can live longer. In Amazon's arc, he and Apollo confront each other again, and Apollo asks for his Perfector back. Tsukasa tosses it to him... then shoots it, breaking it. Now, shooting a guy's only way to keep living may be a dick move, but considering what he did that caused Tsukasa to try and obtain the Perfector in the first place, it's pretty satisfying.
In the penultimate episode of the show, the Queen of the Fangires tells Tsukasa and his friends that he's either with them or against them. Tsukasa gives the Queen and King his usual attitude and leaves. The Queen then sends a Fangire at him. He just simply transforms into Decade and offhandedly roundhouse kicks the Fangire, destroying him in one blow, then tells her that he's the Destroyer of Worlds. Yeah, he just told off the Queen.
That's not the only time he pulled off a Badass Boast about the moniker that Narutaki gave him. When confronting the Big Bad for Kabuto's World, right after he's told that the Big Bad will Take Over the World, he responds with something along the lines of: "Oh yeah? Well I destroy worlds." right in front of the Big Bad.