Geddy Lee: I have lot's of bass, keyboard and technical questions I'd love some answers to, and how certain songs were constructed.
Any and all of these bands: Rush, Led Zeppelin, Black Sabbath, The Doors, Cream, Genesis, Yes: I'd like to just sit in a room and listen to them work on a song, watch ideas develop, see how they work certain parts out, the bass/drum parts, solos, fills, etc.
Trent Reznor: not a huge fan of his work, but the guy is pretty genius with what he's accomplished. Hanging with him would be interesting.
Billy Corgan: never really thought much of him or the band, but after hearing him talk in the Rush documentary I was impressed. I wouldn't mind hanging with him for a day.
John Patatucci, Stanely Clarke, Jaco Pastorius, Flea: wouldn't mind a master class lesson and hanging out later with any of these guys.
Mike Portnoy: he sounds like the kind of dude you can have a few laughs with but still talk technical too.
All the dudes from AC/DC: I saw singer Brian Johnson on That Metal Show and he was a howl with his on the road stories. I'd love to sit in a pub with these guys and just listen to their stories.
And too many more to list...