There are a couple of effects that will effect the pitch of your instrument.
The octave pedal does what it's name says, it shifts the pitch of your instrument by octaves. Some have options as to what octave you want to add. One octave up, one down, 2 down, etc. Then levels of how much original signal and shifted signal to have. The Boss OC-3 Super Octave is an example of a octave pedal.
The pitch shifter is a much more complex unit. There are some pitch shifters that do the same thing as an octave pedal except with other pitches, like a 5th or a 4th. The new generation of pitch shifters let you tell the pedal what key you are playing in and then it can tell if you are doing say 3rd harmonies, if it should be a minor 3rd or a major third, so that your harmony notes are in the right key. The Boss PS-5 Super Shifter and the DigiTech HarmonyMan are examples of this type of pedal.
What do I Use?
Right now I don't have either of these types of pedals on my pedalboard. They are just not what I need at the moment.
Do you use an octave or pitch shifting pedal that I have not mentioned? Let us know in the comments.