In my opinion, the best online self-publishing tool is Blurb. The option to send a link so that potential readers/buyers can see a 15 page preview of the book makes it more user friendly than the other options. I'm particularly fond of their 7x7 books, perfect for publishing photographs. In my quest to become a better photography teacher, I am constantly inspired by the work of Paul Scott at St. Boniface's Catholic College in Plymouth. He is an avid user of Flickr and other web tools to promote the work of his students and encourage them to connect with the wider photographic community. Each year he publishes a snapshot of the students' work using Blurb. Here's a link to the most recent book which is, as usual, a real beauty.