G70 vocal harmonizer is excellent. It will do up to 4 extra voices and all settings can be customized and edited to your liking. Very versatile and very easy to use. It has some excellent special effects and funny voices as well.
Most all functions can be assigned to foot switches and pedals. The dedicated Roland foot controller comes preset to activate all the arranger functions such as variation, fills, intros, endings, or it can be reassigned to countless other functions.
DonM