e-Books

_{Use an e-Book manager like Calibre to manage and convert your e-Books, it provides a good interface.}

General E-Books

Z-Library
Library Genesis (.rs) | .is | .st
Mobilism (.me) | .org - Forum, Requires Sign-up.
MYWAREZ.ORG - Forum, Requires Sign-up.
The-eye - Many e-Books and calibre libraries.
eBook Hunter
Ebookee
OceanofPDF
PDF Drive
Ikindleebooks - MOBIs and ePUBs for Kindle.
My Anonamouse - Has a lot of content, including niche e-Books and audiobooks. Friendly community and mods. Pretty easy to get into.
Project Gutenberg - Legally free e-Books.

Sci-Hub (.se) | .st | .ru
Sci-Hub X Now! (Chromium) - Opens the sci-hub page for the article you want to read.
Zotero Scihub - Addon for Zotero and Juris-M to automatically download PDFs from Sci-Hub.
SciMag - Scientific Articles section of LibGen.
Free Full PDF
Freetechbooks
r/Scholar - If you cant find an article anywhere, you can request it in this subreddit.

Rave Book Search Engine - A search engine that indexes many Comic, e-Book and Audiobook sites.
CALISHOT - A search engine indexing many open Calibre servers, also has a Non English Books Section.
_{If the links stop working check here for updated ones.}
Archive.org & Open Library - Has a lot of niche historical content.
Trantor - Darkweb e-Book resource.
Flibusta - Russian e-Book site.
Yudhacookbook - Contains many recipes and cookbooks.

Bypass Paywalls - Bypass News Article paywalls.
Unpaywall Browser Extension: Chromium & Firefox - When you view a research article, Unpaywall automatically looks for a copy in its index. If it finds one, click the green tab to read the article.
Outline - Removes clutter from News Articles.
Open Access Button - Search engine for research articles.
Browser Extension Chromium & Firefox
Libgen Desktop - Windows application for browsing a local copy of the LibGen catalog.

IRChighway.net/eBooks - Use this guide or their official FAQ to learn how to use the commands.