Decent sized set of pure CSS backgrounds presented in a great UI
Web developer resources
Web development is complex and multi-faceted, therefore a large amount of tools exist to help developers make the most of their time. You'll find some of these below.
The background resources listed below will help you find or generate backgrounds for your sites. Subtle Patterns is a fine example - it's a list of many beautiful minimalist patterns.
The icon resources are either great sources of many icons, or icon fonts. Icon fonts have many advantages, like scalability, and the ability to colour or add shadows without editing an image.
Generate colour themes for your site based on colour theory or mathematically-derived compatibility. Font resources simply provide large amounts of either free or paid fonts. CSS generators let you produce a variety of effects without writing the CSS yourself.
Please feel free to post more if you find something unlisted.
Website background resources
Colour theme generators
Web design blogs