If you're looking for paperback books, you'll find the best deals at Authors Den or Lulu. I like the covers I use on Authors Den a little better than the ones for the paperback as Lulu. Prices are about the same from either place.
If you're looking for hardcover, Lulu is the only place that has them. I have 2 different hardcovers of each book. "Casewrap" means the cover is printed, and "Dust Jacket" means there is a cover over the cover.
If you have a Nook, you'll need epub format. Your best bet is to buy directly from Barnes and Noble. They converted the files to epub, so I know they look nice. Search for Sexton Chronicles in the Nook Book section. Epub files are also available from Lulu, and from Smashwords...but I trust the conversion from Barnes and Noble more than I trust the conversion Smashwords did.
Sexton Chronicles books, ebooks, are available in the Apple iStore, as well as wherever you buy books for the Sony Reader.
If you have a Kindle, the Kindle Store at amazon.com is your best bet. Smashwords sells files for Kindle, but I trust Amazon's conversion for Amazon's Kindle more than I trust Smashwords to do the job.
Here's the part I can control, the part I can promise you: I promise to give you the best adventure I can.