‘Free books!’ Is there a phrase more stirring to the human spirit?
Free ebooks is almost as good.
The main site you want to consult for public domain fiction is Project Gutenberg. Here you can do a keyword search or look through categories like Science Fiction. There are a variety of formats to choose, including EPUB and MOBI.
Project Gutenberg has an Australian counterpart. On this site you can download all the ebooks on each page with Firefox’s Downthemall. Texts come in HTML and TXT, but are easily to converted to MOBI with Calibre.
Downthemall can also download the entirety of Project Gutenberg Canada in one sitting. These ebooks are mostly sourced from the above two Project Gutenbergs.
MobileRead has an extensive collection of ebooks, uploaded by site users in Kindle-compatible formats. The ebooks are meant to be within Canadian public domain, I’d recommend caution on any book that seems too modern. MobileRead also provides a nice hyperlinked ebook that allows you to download any of their files directly onto your ereader.
The Internet Archive has a lot of texts. The available formats vary from text to text, as does the quality and even the legality. Kindle books you get from this site are often badly converted. Project Gutenberg texts can be found on this site, but I recommend going to the original source for those.
I’m certain that I’ve missed a few good sites, and if anyone knows what they are I’d love to receive a link in the comments