Bookshop.org★★★★☆A good place to shop online for books and still support indie bookstores. They sell eBooks too, in standard ePub format.
eBooks.com★★★★☆An eBook seller with some actual business ethics. No hardware (which simplifies things), but they have an app for Android and iOS, and any DRM-free titles can be downloaded and read on just about anything.
Kobo (eBook store and readers)★★★★☆A solid alternative to Kindle, from the eBook selection through apps and hardware. The app works well on my eink tablet without too much tweaking, though it still wants to sell me more books before I can open the one I want to read.
Project Gutenberg★★★★★Predating the web itself, they’ve put together tens of thousands of ebooks from classics and other public domain sources in multiple formats from plaintext to ePub.
Standard Ebooks★★★★★Great source of classics and other public domain material, formatted and edited for maximum readability and compatibility.
Wallabag★★★★☆A read-it-later type service built on open-source software that you can run yourself if you want (but don’t have to). Not as polished as Pocket, but it’s sticking around, and you know it’s not using your saved bookmarks to train a recommendation engine.
Where to Get eBooksA round-up of places I’ve used to find, buy, borrow and download eBooks.