CreateSpace - Amazon.com self-publishing arm allows you to create ebooks and physical books.
Lulu - One of the most accomplished self-publishing sites.
Rudy Rucker, a retired math/computer science professor, prolific science fiction writer, and e-book novice wrote up his experience in publishing Ebooks in these four blog posts (which he then published as an Ebook through his own Transreal Books).
How to Make Ebooks #1: Getting Started
How to Make Ebooks #2: The Simpler Paths
How to Make Ebooks #3: Medium Level: Calibre & Sigil
How to Make Ebooks #4: Advanced Level: Dreamweaver & HTML