My most brilliant kill was on Harvest, as Classic Demoknight.
I have the habit of always chargejumping to the second floor of the enemies house, by hitting the vaguely ramp-like prop at a certain angle. This led to many other awesome kills, like going straight to the window right in a Sniper's face for example. But my favorite is a bit more unlikely.
Well, as I am lining up for my charge at the 'ramp', I spot a Rocket Jumper Soldier on the roof, who is at the exact spot I've chosen to land on. He proceeded to rocket jump just as I chargejump.
I cross his path in mid-air, and thus plonk him with my sword. Due to the charge, I score a crit. In mid-air. But this does not kill the Soldier, as he hasn't lost any HP before the mid-air collision, instead he gets send into the skybox with a speed rivalling the launch of a NASA Rocket.
Meanwhile, I land on the roof and turn around to see where the Soldier went. It took a full five seconds for him to come down and crater next to the shack with the Medkit., which obliviously killed him as he had five hp left. I just watched in awe.