Hero Patterns - A collection of repeatable SVG background patterns
TexturePacker - Texture Packer is hands down the best sprite sheet generation tool on the market.
MagicPattern - The best design toolbox with 10+ tools for anyone
Free Texture Packer - Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites.
Adaptive Backgrounds - Extract dominant colours from images
Sprite Monkey - Small and fast but still full-featured sprite sheet editor.