Here is scope for ingenuity. Let people of shrewd intelligence calculate the number of the Wild Beast; for it indicates a certain man, and his number is 666. (Weymouth New Testament)
The best interpretation I've seen so far is from Conte's The Bible and the Future of the World. He thinks the number represents the first, middle, and surname's of Antichrist. Each will be six letters long. He also notes that some Bible versions passed down to us have 616, and that this is providential for it hints that the middle initial is abbreviated like some do in these modern times.