Pitch Shifter - The pitch shifter is one of the most versatile effects in the pitch category. It can be used on a foot pedal for up and down pitch shifting (dive bomb) or a pedal that can detune all strings at once. This comes in handy instead of using a capo or tuning low for modern death metal. 

Harmonizer takes the original signal and adds in shifted pitch. A great example is the opening lick by Prince in the song "When Doves Cry"