I previously forgot to mention that in my Stumbling that I have also come across Project Gutenberg and Librivox. Project Gutenberg has a larger selection of eBooks than Planet eBook, though they're not all available in PDF format. Personally, I prefer the formatting from Planet eBook, but that's just me. I'm not discriminating against Project Gutenberg for their formatting.
Librivox is literally translated from Latin as "free voice." That being said, it's a catalog of free audio books. The selection is quite varied, but all of the books are, like Planet eBook and Project Gutenberg, those that are in the public domain.