Rainbow Dash's spotlight comic starts off with her pulling off a Sonic Rainboom while playing an electric guitar. If that's not cool enough for you, how about a Sonic Double Rainboom all the way, across the sky?
If not even that is awesome enough for you, how about the fact that said Sonic Double Rainboom also severely damaged her wings, making this also a bit of a Heroic Sacrifice. She gets better after two months of no flying, though.
The battle in the flashback in the Celestia's issues. Celestia shows some serious battleskills, even better when joined by Inkwell.
After making his mail order Sea Beasts sentient, Spike goes on to accept responsibility for the little buggers, turning them towards peace when they discover war, and educating them in the ways of many great Equestrians. The final result is a peaceful, enlightened people who desire to go out into the world on a quest for further knowledge. Spike played God, and he won! How many other characters, in all of fiction, can claim to have done that?
After Flim and Flam have been aggravating Karma Houdinis whenever they've showed up before, it's quite satisfying to see Luna take them down a few pegs, Solomon style.