The American Mathematical Society publishes Mathematical Reviews, perhaps the most important single resource for mathematical research in existence. As part of this, and presumably for fun, they have constructed the MR Collaboration Distance page, where you can use their database to find out how closely any two people are related through a string of co-authors. It's great fun! Here are some that I ran (on 10/14/04):

From me to:

R.H. Bing: 6
Larry Conlon: 7
H.S.M. Coxeter: 4
Paul Erdös: 4
Ralph H. Fox: 6
David Gabai: 5
Allen Hatcher: 4
David Hilbert: 8
Mikhael Gromov: 5
John Milnor: 5
George Mostow: 5
Peter Scott: 3
Herbert Seifert: 7
John Stallings: 5
Bill Thurston: 4
Andrew Wiles: 6

And some of my fellow faculty members:

George Avalos: 7
Lucho Avramov: 5
Allan Donsig: 6
Lynn Erbe: 6
Susan Hermiller: 4
Wendy Hines: 7
David Logan: 6
Tom Marley: 5
John Meakin: 6
Al Peterson: 6
David Pitts: 6
Jamie Radcliffe: 5
Mohammad Rammaha: 7
Richard Rebarber: 6
Judy Walker: 6
Mark Walker: 6
Roger Wiegand: 4
Sylvia Wiegand: 5
Gordon Woodward: 6