Delay - just the really boring one called Delay that comes with Protools is my toy of the week. It's letting me turn drums into pitched instruments, like a 14.44ms delay gives you a C# if you feed it a small enough piece of a drum and set the feedback to 80-90% ... think BT and you'll be there. It's like really simple granular synthesis.

Make the delay times left and right + and - a few milliseconds and low and behold you have the same effect in stereo!