HTML & CSS:

Image Overlay Effects- Adding little labels/overlays of text to your image.
List Styling- Styling a list like this one!
Grid Template Areas- How to use the grid template area layouts.
Google Fonts- Easy to use web fonts.
Free HTML Formatter- Easy way to style your messy HTML if you're new to coding.
Teppy's Layouts- Quick and easy layouts and guides to get you started on Neocities!
Postimages- Best image hoster on the web imo.
CSS Dropdowns- How to make a simple dropdown button with css.

Graphics:

Chaicons- A bunch of small f2u pixel icons.
Blinkies Cafe- Blinkie maker and archive.
Junabuggy's Masterlist- Master list of blinkies, stamps, and other web graphics.
WandaPinkay's Buttons- Free/PWYW buttons for your page.
Unsplash- F2U images for backgrounds and shit.

Misc: