My friend and colleague Larry Hurtado (University of Edinburgh) has written a brilliant and important book entitled How on Earth Did Jesus Become a God? Historical Questions about Earliest Devotion to Jesus (Eerdmans, 2005). It is a more popular version of perhaps his most well known book, Lord Jesus Christ: Devotion to Jesus in Earliest Christianity (Eerdmans, 2005).
For those who want a 10 minute distilled version of his thesis, take a look at the video here. It is the best summary I know of his big idea!