My best kill/takedown was actually in Burnout Revenge.
One track (I forget the names now) had a really long tunnel cut through the side of a mountain, and the right wall of the tunnel is kind of curved (like it gradually gets steeper until it goes vertical).
In Revenge, when you get a takedown in specific areas, it gives you 'signature takedowns', and takes a quick snapshot of the takedown, as another collectable to lengthen gameplay. (Unfortunately it doesn't save the actual snapshot) This tunnel was one of them.
I had been battling another driver the entire length of the tunnel, never quite hitting hard enough to take him down, until, at the end of the tunnel, I got some momentum, and managed to push him up the curve of the wall, causing him to do a barrel roll, directly over my car. When the game paused and zoomed in, his car was directly over mine, our vehicles perfect mirrors, mere inches apart.
Not really a kill, but it was pretty cool to see.