This is an ever-growing list of links I've collected over time, ranging from resources to fun stuff, which will hopefully benefit you now too :p
Everything on this list should be free, or was at the time of adding. If I find out otherwise, I'll probably remove it.
This bit will be the most extensive: templates, guides & code snippets. Please see kicya.net and WidgetStar for awesome indie web resources!
Guides
PetraPixel First Steps
You'll be seeing this name a lot, because they have a lot of good stuff. See also: beginner tutorials (this was how I learned grids).
w3schools
Has references and examples on every HTML & CSS function. You'll want to refer back here frequently because you will not remember every tag and attribute off the top of your head.
MDN
Mozilla has it's own web developer guide site - I've linked the CSS layout cookbook, but there's so many other useful things on the sidebar too.
Templates & Layout Generators
PetraPixel's Layout Generator
Easy to use, mobile responsive layout generator, with a ton of awesome resources to boot!
America's Decline's Free Web Layouts
Gorgeous, free to use web layouts for your website. Make sure to read the usage guidelines.
Teppy's Layouts & Tips
A bunch of cool, varied templates. Some of them use iframes, so make sure you read their tutorial so you can use them right!
Createblog Website Templates
Free to use website templates submitted from 2006-2012. (Some are a little broken)
Houdini's Layouts
Small collection of wildly varying web layouts. Remember to link back to their site if you use them!
HTML5 Templates
Includes interactive windows and a Wikipedia article mimic.
Jansite's Templates
A cute responsive web-style layout, and a wikifarms style layout (think Fandom Wiki or Miraheze)
Code Snippets
Loveberry
Cool boxes/borders, text effects and other code snippets.
PetraPixel code snippets Stuff like consistent header/footer across pages, automatic table of contents, redirect, etc.
Anything to do with visuals will be here. Can be used for web, but also elsewhere.
Delphitools
Awesome collection of tools including a background remover, palette generator and QR Generator, but also a bunch of calculators, a watermarker, a regex tester... just go and look.
BlinkieWiki
Huge, searchable directory of mostly blinkies, but also stamps, favicons and buttons. Left click to view credits & other data!
Stamp Studio
Easy to use stamp maker, compatible with images and gifs.
The Cyber Vanguard
Their 88x31 button collection and mirrors section are what you're looking for, but they also have cool articles on programming.
Pixel Safari
Neat collection of graphics including stamps, favicons and blinkies.
88by31
Collection of decorative 88x31 buttons.
xixxii "a rummage bin"
Interesting collection of graphics, including backgrounds, custom div borders, page borders, and layouts. They have an awesome site too, so go explore it when you're there.
Luna's F2U Goodies
A collection of free to use & edit graphics, including tiled backgrounds, cursors and fonts.
TextureTown
Collection of repeating background textures.
SMALL PIXELS
Collection of 20x20 animated pixels.
Rotating Food GIFs
Collection of rotating food gifs, the first of six collections.
Online Image Editor
Lets you edit images in an array of ways, most importantly by adding obnoxious glitter.