Cozy Powell. Modern Drummer said it best by stating that Cozy never reached Bonham like status because he was never associated with one band like Bonham or Paice.
Tommy Aldridge is another drummer associated with multiple bands and a great talent who is probably not given enough credit.
I am not sure Alex Van Halen received the credit he deservedmay be overshadowed by Eddie and contemporaries like Peart.
On a smaller level there was Frank Briggs from an 80s upstate New York band called 805. I was lucky enough to see them many times and Frank was mesmerizing. He has gone on to record with his own band and perform at clinics. Check out http://www.youtube.com/watch?v=6k67ptMisUM&feature=related and watch his solo from 1986 (amateur quality). The first 4 minutes or so he plays melodically on Simmons drums which were popular at that time. If you do nothing more, check out from about the 6:30 mark and watch his snare drum work and amazing patterns between the snare, bass drum and china cymbals.
