I listen to way too much music to have one favorite band. Here's some though off the top of my head though for each genre

Metal: Slayer, Metallica, Iron Maiden, Anthrax
Punk: Misfits, Rancid, Operation Ivy, The Clash, MDC
Ska: Reel big fish, Mephiskapheles, Big D and the Kids Table, The Planet Smashers
Hip-hop: Sweatshop Union, Common Market, One Be Lo/Binary star, Quasimoto, Public Enemy, Eminem
Classic Rock: Led zeppelin, Pink Floyd, Rush