The EPUB and KindleGen tutorial originally written last year is one of the most viewed pages on this site. I believe the reason for this is that the information online is relatively sparse concerning this open eBook standard. I spent some time working on a new tutorial for building an eBook from the ground up, without the use of third-party software. The result is the EPUB and KindleGen tutorial on the BB eBooks website. There are also EPUB samples that you can download for your eBook projects on our Developers page.
Please let me know if you have any feedback or questions on it, and I hope that it helps eBook designers create better eBooks.