Sign up at the Flickr website and open an account (free).
Take the cover of your e-book in several versions and sizes and load them up at the Flickr website. Write lots! of good tags to describe these photos of your e-book. Flickr allows you to up to 75 tags to each photo. Which means: 75 possibilities for people to find, and learn about your e-book.
Tags for e-book photos could be for sample: E-Reading, Kindle, Sony, Kobo, Nook, ereading, e-books, ebooks, ebook online, book cover, digital display, electronic book, information medium, publishing, reading, text, textbook, internet, author, technology, books, education, literature, paper, media, writer, self-publishing, e-Reader, writing news, tablet computer, iPad, e-book conversion, … and most important: the title of your book and content words (tags) in various versions.
For even more exposure of your e-book photos (but only if the cover is really professionally designed and in high-resolution) join the FotoVotr.com Amber Group.
A free and easy way to show your e-book to the world!
P.S. The book cover image above is a (German) title that I wrote years ago and very successfully self-published and marketed. I will publish it as an e-book next month.