I met Kenny G in the pit at the Opeth show last month.
Are you serious?? I never would have pegged him for being an Opeth fan.
As for my list, a few, but not a lot. Here's what I can recall:
Queensryche - Geoff Tate, Michael Wilton, Eddie Jackson, Scott Rockenfield
Lacuna Coil - Andrea Ferro, Cristiano Migliore, Marco Coti Zelati
King's X - Doug Pinnick, Ty Tabor, Jerry Gaskill
Y&T (past and present members) - Dave Meniketti, Phil Kennemore, Joey Alves, Leonard Haze, Stef Burns (yes, the same guy who was in Alice Cooper, Huey Luis & the News, etc.), Mike Vanderhule, John Nymann (I think I also met Jimmy DeGrasso at one point, but I don't recall for certain whether we actually spoke or just passed by each other at a show)
Transatlantic - Neal Morse, Roine Stolt, Mike Portnoy, Pete Trawevas, Daniel Gildenlowe (also met Neal's drummer, Colin, who was serving as TA's tour manager at the time)
Britney Fox - Michael Kelly Smith
Jeff Scott Soto
Dave Meniketti Band - Myron Dove, Chris Miller, Tony Stead
I also emailed Charlie Dominicci a bunch for a while, but never met him face to face