There are definitely a lot of photography ebooks in the wild right now. The one thing I've noticed though about those, is that most of them assume you're more of an intermediate/advanced photographer, and a lot of them can be hard to follow with photography terms that no one but the expert would understand.
I'd like to introduce Suburbia Press, who, with their first two ebook offerings, has made it clear that the world hasn't forgotten about the novice and early intermediate photographer. Suburbia Press is the brainchild of William Beem, who many people know is very active in the photographic community (he also is a staple of NAPP, having attended many a Photoshop World). All the books are in PDF format, so they'll work wherever you can view a PDF file - computer, tablet, even your smartphone.
First up is Basic Photography Techniques. This covers everything someone new to photography (and even someone who wants to learn more about how things work) needs to know about topics such as focal length, exposure, f-stop, and shutter speed. With its fun layout, prominent headers, and information written so anybody can understand it, the use of photos really adds to explaining the topic at hand.
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Secondly is a book that's a little more intermediate, but for those interested in workflow: Professional Photography Workflow with Aperture. The first section of the book talks about digital assets and workflow in general, which is fantastic information for anybody wondering about that. Then it gets into Aperture proper going over topics such as organization, reviewing photos, Aperture vaults, and of course, creating your Aperture structure. This book is definitely more for somebody looking to get into photo organization, and doesn't go into technical photography. While it may be geared more toward the intermediate user, I'm convinced that the novice user will still learn an insane amount of information.
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Suburbia Press is an ebook company that's coming out with guns blazing, ready to tackle the photography ebook market. They have many more offerings in the works including photography travel guides from Las Vegas, Disney, Washington D.C., as well as ebooks on lighting and more advanced Aperture. I highly recommend everybody check them out.