ConvertIcon! - Converticon is a simple icon utility.
TexturePacker - Texture Packer is hands down the best sprite sheet generation tool on the market.
GenFavicon - Generator Favicon.
Sprite Sheet Packer - Sprite Sheet Packer is online that you can easily use to pack sprite sheets, including data formats for CSS, LESS, and Phaser.
Ordinatore - Those who want to tidy up their Macs will surely love this application.
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.