Most extreme metal drummers cite the usual suspects as influences - Dave Lombardo, Gene Hoglan, Pete Sandoval, etc.  Going through some of the interviews at SickDrummer.com, I noticed a couple of unfamiliar names coming up repeatedly: Buddy Rich and Dave Weckl.

Buddy Rich was a jazz drummer who gained prominence in the 40s and 50s.  Dave Witte (Human Remains, Melt-Banana, Burnt By The Sun) described him as "the greatest drummer to ever live."  Richard Hoak (Brutal Truth) and Derek Roddy (Nile, Hate Eternal) also counted Rich as an influence or favorite.

Videos of Buddy Rich abound on YouTube.  Here’s Rich performing a solo: Buddy Rich Drum Solo

Dave Weckl is a jazz fusion drummer who seems to be extremely well known among drummers; the list of drummers citing him as an influence is impressive: Dave Culross (Suffocation, Malevolent Creation), Derek Roddy again, George Kollias (Nile), Ken Schalk (Candiria), Sean Reinert (Cynic, Death), Tim Yeung (Decrepit Birth, Hate Eternal, Vital Remains, Nile), and Danny Walker (Intronaut, Uphill Battle), among others. 

Here’s a video of Weckl performing: Dave Weckl Performance on YouTube