Additions are welcome! Please post in the comments if you're missing any. While I realize other sources and shadow libraries exist, I want this list to be about supporting the sites, stores and authors that make an effort to supply legal, DRM-free alternatives.

Ebook Stores

Ebooks.com DRM-Free section

Weightless Books (Sci-Fi magazines)

StoryBundle

Smashwords

Angry Robot

Delphi Classics

Humble Bundle

Kobo's DRM free section

Publishers

Tor Books

Baen Books

Authors

Cory Doctorow (Sci-Fi)

Greg Egan (Sci-Fi)

Honor Raconteur (Fantasy/YA)

Juliet Marillier (Fantasy)

Brandon Sanderson on Bookshop.org (Sci-Fi, US-only)

Brandon Sanderson on eBooks.com (Sci-Fi)

Libraries

The Anarchist Library

The Internet Archive

Project Gutenberg (American/General Public Domain, has many other countries and languages as well)

Project Gutenberg Canada (Canadian Public Domain)

Project Gutenberg Australia (Australian Public Domain)

Standard eBooks (Formatted Public Domain eBooks)

French eBooks

Ebooks libres et gratuits (French Public Domain)

French Bibiliothèque Nationale's Gallica (French Public Domain)

Les classiques des sciences social, with a large selection of essays and academic papers

La bibliothèque numérique Romande (Swiss fiction)

7switch

Le Belial (Sci-Fi/Fantasy)

Dystopia Editions (Sci-Fi/Fantasy)

Nordic eBooks

Litteraturbanken (Swedish Public Domain)

Runeberg (Swedish Public Domain)

Nasjionalbiblioteket (Norwegian Public Domain)

The National Library of Finland (Finnish Public Domain)

Audiobooks

LibriVox (Narrated public domain eBooks)

Libro FM

Games

GOG

Itch

Zoom

Music

Bandcamp

7digital UK/7digital US

Qobuz

Honorable mention, SomaFM: free and non-commercialized internet radio.

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A note, if your native language is for example German, Swedish, Norwegian, Danish, Polish or similar, you can usually find DRM-free ebooks in your native language through your national stores. The ePubs are usually just watermarked. This might be applicable to other countries as well, even though I'm aware that some countries like Japan or South Korea have even stricter DRM schemes than the English-speaking world.

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