Bo Jackson! War Eagle!
B. B. King
Bert Lahr
I refuse to say the first name that came to mind (Manilow), so:
Billy Mays
Bill Nye the Science Guy
Beat to it
Brian Orser, figure skater
Biff Pocoroba, Atlanta Brave
Brady Quinn (Denver Broncos quarterback)
Bob Ross, TV painter
Bob Ross (and all his happy little trees)
B.O. and you came up with Brian Orser? You couldn’t think of any other “famous” person whose intials are B.O.? No one? Of course I mean Bill O’Reily 
Boz Skaggs
Bernie Taupin
Blair Underwood
Brenda Vaccaro (the first woman to be mentioned in all the B’s)
Betty White
Brian Xavier (technically, fictional)
Bobby Yarborough (motorcycle racer)
BZ
Bob Zimmerman (Dylan)
Charles Atlas (muscle man)