1. Boss MO-2 Multi Overtone
Blamgggggg. That's the sound the MO-2 Multi Overtone pedal makes... and I love it.
It's like a harmonic exciter if you use it sparingly, breathing life into your tone, or you can turn it up in the mix and get the huge harmonic overtones you get from Hammond organs.
It's a little box of tricks, and I can't recommend it enough (and yes, I did buy one)!