I don't really like the wizard Disc books--I like the witches and the Watch, pretty much. And I don't totally like him for the humor (although I do find him funny), but also the other stuffs--the odd little insights into human nature, the surprisingly moving bits.

Anyway, what I think are the main characters people might write about (and not making the list too long):

Agnes Nitt/Perdita
Christine
Walter Plinge
The Ghost
Andre
Granny Weatherwax
Nanny Ogg