DigiTech Studio Vocalist EX

This is the exact model used by both Daft Punk for Digital Love and Imogen Heap for Hide And Seek.

That was enough for me to track one down for my studio and keep it forever, but now we have a second. They're not very common, and only the EX will get you where you (may) need to go...

I always thought both those tracks were vocoders, but nope - it's this very cool and very unique-sounding midi harmonizer/pitch shifter.