Generally I think most people consider the main theme to be about Buddy Holly. But the posted link above offers lots of other references throughout the song.
Don McLean has never revealed the exact meaning in his most famous song. I interviewed him last year, and again he politely dodged the question, which he must be sick of hearing! the general concensus is that it's about the death in a plane crash of Buddy Holly - a lot of the lyrics back up this notion.
I asked him what he thought of Madonna's version, and he reckoned that anything that increased the profile of his work was a good thing.
His missed his vocation - the United Nations could use diplomacy like that!
Overall I think it is about the birth and growth of rock music
When he says "for ten years we have been on our own" I think he is refering to the rock and roll business when it broke away from middle of the road popular music.
Throughout the song there are references to Buddy Holly, Elvis Presley, Bob Dylan, The Beatles, the Rolling Stones, The Byrds and so on.