SubtleSonic Super6 Detune
Super6 is a detune plugin based on a reverse-engineering of the Roland JP-8000 SuperSaw oscillator. The original SuperSaw oscillator used 7 stacked detuned sawtooth oscillators to produce a fat wave; three oscillators are tuned below the fundamental, and another three are tuned above.
Super6 takes audio input and uses pitch-shifters to achieve similar effects for any signal. It can produce everything from subtle chorusing to nasty detunes, so if your synth sounds a little thin, Super6 can fatten it up.
It’s not free, but it is very cheap ($5, quick and easy and no Paypal required) and it works in Live 8 / Max 5 and up.
The project is written entirely in Max for Live.