I'd say the coolest athlete I've ever met/lived next to was Bob Cousy. He used to live like 10 houses down from me one the same street in Worcester, MA. Guy is the man.
Also, I met Adalius Thomas at TF Green Airport in Providence, RI the first year we signed him. Not the greatest, especially since he was terrible for us, but still that was pretty cool.
And finally I never met him, but my uncle met Big Papi. My uncle is a state cop and one of his friends somehow managed to land a job as a body guard for Papi one night in Worcester. My uncle said he was one of the greatest people he has ever met, just full of life. Anyway, I got a signed baseball out of it, pretty cool.