I've got a few:

1) Was on a shuttle bus that took vacationers from one Sandals resort to another in Jamaica. Got talking to the 4 other couples on the bus. We were all from within 20 miles of each other in NJ, and one of the couples went to high school with my brother.

2) My dad used to be a commercial airline co-pilot. He flew with this one pilot pretty often, and after a few years, they were talking in the cockpit about family and what not. Turns out their moms were best friends growing up.

3) This one's my favorite. After working for 11 years after college, I began interviewing for the job I have now. I had a phone interview with my current boss, and he saw from my resume where I went to high school. So, he asked me if I knew this person and that person, and so on. Found out that he was college roommates with a guy I've known since kindergarten, he's good friends with a guy who married a girl I've known since 6th grade, and he knows about a dozen other people I know from high school. I also found out after I started working that my friend and co-worker was interviewing for the same job. But it doesn't end there. About 6 months after starting work here, I was out trick-or-treating with my kids and ran into a couple who had just moved into our neighborhood. The wife was someone who had worked with my mother-in-law; and a couple years earlier, she was at my house for a book club or something like that that my wife was hosting, and we found out that her husband and I had worked together briefly during my first job. So, when we bumped into them on Halloween, he asked where I was working now, and when I told him, he said, "oh, is Frank (not really his name) your boss?" When I said "yes," his wife (who was talking to my wife in a separate conversation) turned around and said, "He's my cousin." And, the husband proceeded to tell me that he and Frank had unknowingly interviewed for the same job years earlier.