Webdev

The Bibble.
Stack Overflow If you have a question about code, you'll probably find the answer here
Code Beautify Make your code look pretty
JS and CSS Minifier Make your JS and CSS tiny
Codepen Online code editor with a live preview.
Glitch Same as codepen, although I prefer this one, especially since you can do a lot more.
Contrast Checker Check the contrast between your text and background.
HTML Cheatsheet A very helpful site to have while coding.
CSS Gradient Make gradients with CSS.
DaFont Lotsa fonts.
98.css, XP.css, 7.css CSS frameworks for windows styled boxes and other things. I used 7.css for my about page.

Code Snippets + Widgets

FC2 counter Free visitor counter + online viewer counter for your site! You can even make a custom one.
RV's free effects Lots of cool effects for your site!
imood Share your current mood on your website with a widget!
Status Cafe Share your current status... on your website... with a widget!
Cbox Put a chatbox on your site!
Button Sound Play a sound when you click a button.
JS Emojis Custom emojis that can be displayed with text. Made by freakphone.net!
WebAmp w/ skin Put a WinAmp on your site!
Gifypet A cute little pet that you can take care of for your site!
Tamanotchi More cute pets! Visitors can feed your tamanotchi so it can grow!
Last.fm Widget If you use last.fm, you can use this on your site to show what you're listening to!
Dress up Game Tutorial Make a dress up game with html, css and js!

Graphics

Lots of cute pixels that are free to use.
Lots of cute pixels that are free to use.
Create your own blinkies! Lots of cool templates to choose.
Gifcities A bunch of gifs archived from old geocities websites
Hekate's Background Archive Lots of great "old fashioned" tiled background for your website!
Free Backgrounds More backgrounds, used this when I first started this site!
Glitter Graphics A ton of graphics, includes some text generators
Web Badges World Huge collection of web badges.
88x31 GIF Collection [Flash Warning] Huge collection of... 88x31 gifs

Useful Tools

A flash player emulator. I use this to host playable swf files on my site!
Kirupa.com Old but very useful flash tutorials. Great if you want to make flash games! I reccomend using ruffle to see the examples.
Remove Background Remove backgrounds from images...
Yout Download youtube videos.
Cloud Convert Convert your files to other files
waifu2x Image scaler for anime art
Online Text Tools A shit ton of, wait for it, text tools!
Image Color Picker Get hex codes by picking colors from an image! I use this a lot
UPNG Make your pngs (and other image types) tiny. Good if you don't want images to take up a lot of space on your site.
Online Image Editor A great image editor that has a lot of neat features.
Twine Create interactive stories.
Perchance Create random text generators.

Archives

Shouldn't have to explain this one.
Animate Archive Different versions of Adobe Flash.
Flashpoint A huge library of old flash games and animations.
OoCities Old Geocities sites.
Web Design Library Old web design.
Phatmedia Old rave flyers.
Winamp Skin Museum A library of... Winamp skins.
MyFigureCollection Database of anime/video game figures and goods, great for keeping track of your own collection.

Art

Wick Editor Free tool for creating games and animations in your browser, similar to flash.
Piskel Make pixel art and sprites online.
Drawabox Free drawing lessons.
Settei Dreams Bunch of model sheets, color sheets, artbooks, etc
JS Paint Classic ms paint in your browser.
JS Kidpix Kidpix in your browser.
Shake Art DELUXE Make shaky art.

Gaming

zenius-i-vanisher.com/ Look up arcades in your area and see what games they have + the quality of them too!
My Abandonware Download and play old games. I got Kid Pix here.
Minecraft Tools Bunch of commands and tools for Minecraft.
ACNH Island Planner An island planner for Animal Crossing New Horizons. People still play that, right?
noclip Explore 3d maps from various video games.
Fancy Island (AKA Lomando.com) A horror puzzle game. Contains jumpscares.
lain game The Serial Experiments Lain video game in your browser.
LSD Dream Emulator LSD Dream Emulator in your browser

Fun

A virtual pet site with forums.
A virtual goat site with forums.
neal.fun A collection of fun interactive stuff.
aidn.jp [Flash Warning] Website of daniwell. Also has lots of interactive stuff.
charat.me Lots of cute avatar creators/dress up games.
ktestone.com Lots of cute personality tests. Accurate? Probably not.
objection.lol Turn you and your friends conversation into an Ace Attorney case.
Shimeji Silly guy that runs around your desktop. You can find shimeji of lots of characters, and even make your own.
WINDOWS93 Le epic operating system
plaza.one Vaporwave radio, used to listen to it a lot in middle school lol
Online Omnichord Play an omnichord!
petpet generator petpetpetpetpetpet
The most amazing website on the internet [Flash warning]