Note: some mirrors of the pages linked below may not work. Please lmk if there are dead links!
R74n: I used to go on this site. Contains some very useful tools and games and pixel art. Too bad it's full of Google ads now. (GitHub page)
Spyware Watchdog (TOR) (I2P) (Freenet) (Zeronet): very useful if you want to check software for spyware. (Git Repo)
Shadow Wiki (TOR) (I2P): Largely inspired me on making my blog. Contains some very nice tips about anonymity, and gives advice on browsers, email providers etc.
Diyar Ciftci (Clearnet) (TOR) (I2P): Another blogger I have read. Also includes some good articles about privacy and anonymity. Also includes some useful tools (such as a link shortener).
Richard Stallman: A director of the Free Software Foundation and the Chief GNUisaince of the GNU Project.