My band's album uses 3 tunings - drop C, D standard and drop B. I switch between standard and drop tunings fairly often, simply because some things play better in one than the other.
Soundgarden changed tunings all the time. I think there's about 4 or 5 on Superunknown - standard, dropped, dropping the E 2 steps and the A 1 step, open G and I think they used all E too (though I think that was just for a natural harmonics section), and that album sound consistent.
Steve