The only PHP5/OOP book I've read is PHP Objects, Patterns, and Practice by Matt Zandstra. It's pretty good, but I'm not sure I would recommend it for beginner level programmers, unless you are only a PHP beginner but have at least some prior experience with other OO languages.
PS: I just noticed that you specified "ebook". I do not know if the above is available as such. I do know that www.oreilly.com has most of their books available as ebooks, and I'm sure they have a number of PHP/OOP books.
