I had a few, mostly because they kept vanishing.
At Primary School my best friend was Kevin Craddock. Kevin lived a couple of roads over, and gave me one of his guinea pig's piglets (?). Unfortunately his dad moved to North Yorkshire to get a new job at the end of Primary School. I went and stayed with Kevin in North Yorkshire during a school holiday, and loved it so much I didn't want to leave. I remember crying in the car on the way home. I never saw Kevin again, and we lost touch.
At Middle School I managed to recover and find a new best friend, Lindsay Jones. Lindsay lived in a neighbouring village, and his parents were both teachers at a local private school. He was the classic cool best friend, and introduced me to some great music, books, and films (his dad was a drama teacher, and had an *awesome* VHS collection), air pistols, and fireworks. Then in the third year of middle school he left and started at the private school his parents worked at. We kept in touch initially, but then drifted apart. We met again on Facebook, but nothing has come of it. He now lives in Germany.
I didn't really have a best friend for the remainder of Middle School, and also the first couple of years of Comprehensive School - 4 years which were a fairly dire time for me. Then I met Ben Cox, via the social circle I was in. Ben lived about a mile from my parents' house, and we had a mutual love of computer and roleplaying games. We were best friends until around two thirds of the way through the second year of 6th Form College when we had an argument, and following that I had a girlfriend I dedicated 100% of my time to (stupidly). We drifted apart fairly rapidly, and that was the end of that. We met again on Facebook, and despite BBQ invites and talk of meeting up (he now lives in his parents' house with wife and two kids, so I assume his parents have gone elsewhere) nothing has come of it.