Well, the Gorillaz have a pretty sweet website... http://www.gorillaz.com
From what I remember, the Gorillaz consists of:
Dan the Automator: DJ, producer
He's done a lot of work in the Hip Hop realm... was in another group called Handsome Boy Modeling School
Miho Hatori: Guitarist (Noodle)
Part of Japanese group Cibbo Matto
Del tha Funkee Homosapien: Guest Emcee
I can't remember the other member's names off the top of my head... but I know all of them have done their own stuff for a while before joining together for this project.