E-books are not an accepted format to many authors, they feel threatened that they are releasign thier work in an easily copied and "pirated" format. Most of the e-books that are released are either old public domain or the authors are willing to take a chance and build loyalty. Most notably are the SF authors, go to
www.baen.com and you will find a wealth of free and low cost first run e-books. There are a number of other sites that will sell E-books but the available books are still slim and your favorite author may not be allowing thier work to be put out in this format.
Amazon.com also sells a large number of e-books. You can do a web search for other sites. Bottom line is that at this point in time E-books are just starting to catch on so its still a "Crap" shoot on what and who is released in the electronic format.
Good Luck.
