Hey, I just realized I haven't posted my list of websites for creative backgrounds here on dev.to yet - so here it is:

SVG Backgrounds

A list of easy customizable SVG backgrounds.

Gradient Magic

A huge collection of SVG pattern backgrounds by Steve Schoger.

pattern.css

A cool css library for background patterns, which can be easily applied to all elements.

Trianglify

A generator for low poly triangle patterns.

Transparent Textures

A large collection of CSS patterns, which can be filtered and colorized.

Ambient Canvas Backgrounds

A bunch of nice backgrounds using the HTML5 Canvas API.

Hero Patterns

Repeatable SVG background patterns by Steve Schoger.

css-doodle

A web component for drawing patterns with CSS.

particles.js

A lightweight JavaScript library for a particles background.

Pattern Generator

A cool generator for unique, royalty-free, repeatable SVG patterns by John Bartlet.

The Pattern Library

A compiled list of beautiful patterns by different designers.

SVG Gradient Wave Generator

A generator for SVG wave patterns.

Subtle Patterns

A huge list of more than 500 subtle background patterns and textures.

THPACE!

A pretty space animation out of triangles using canvas.

Background Generator

A cool generator, which also has a small list of backgrounds created with it.

Naker

Create interactive backgrounds on this website.

Vanta.js

Animated WebGL backgrounds with the possibility to customize.

Gradient Backgrounds

A website, which combines the most popular gradient collections.

GeoPattern

A generator for beautiful SVG patterns.

Decorative WebGL Backgrounds

A collection of shapes created using WebGL.

CSS Waves

A smoothly animated wave with pure CSS.

CSS Gradient Animator

A site to create beautiful animated gradients for use on your website.

Flat Surface Shader

A configurable lightning simulation using canvas or SVG polygons.

Animated Background Headers

Creative website header animations using Canvas and JavaScript.

Animated CSS Background Generator

A collection of pure css animated backgrounds with the possibility to customize.

Did I miss anything? Let me know in the comments :)