A few for me that have been lengthy interactions and not just a quick meeting:
Red Auerbach - my boss at GW was the son of Sam Jones, Celtics HOFer. Red is a GW alum and would be at the Rec Center all the time. Played racquetball with him a couple times.
Sam Jones - played golf with him a few times
Dan O'Brien (decathlete) - he's the only famous person that has approached me. He was hired by Andre Agassi to help promote a new fitness company Agassi owned. I worked at Oregon at the time and we were buying about $250,000 worth of fitness equipment at the time. He approached me at a trade show (he's from Oregon) and wanted me to come over to Agassi's fitness place the next day. Sent the stretch hummer limo for me and everything. Was pretty cool.
Ted Leonsis - owner of the Capitols and Wizards among other things. Very cool guy. We have a mutual friend and when I worked at Penn, his son was going to be a Freshman there. Struck up a conversation and chatted for about 15-20 minutes. Gave me his business card (he was the Vice Chairman of AOL at the time). Ran into him at the airport in Vegas a couple years later. Was surprised he remembered me.
I've met a number of college basketball coaches, announcers, personalities, etc. from my time running the Palestra in Philly. If you ever get a chance, I highly recommend seeing a basketball game there.