A group? The Who or Dream Theater (great choice OP). Both have a huge range that they've played over the years and they're both up there with my favorites.
One person? Trent Reznor, Maynard Keenan, BT or Mike Patton. All of them have a ton of projects that again span many genres.
EDIT: The final choice would probably be BT, by the way. Considering he's done my top 2 albums of all time I'd call it a safe bet.
Edited by MorbidToaster - 7/14/12 at 7:24am