ImageOptim

ImageOptim optimizes images — so they take up less disk space and load faster — by finding best compression parameters and by removing unnecessary comments and color profiles. It handles PNG, JPEG and GIF animations. It’s excellent for publishing images on the web (easily shrinks images “Saved for Web” in Photoshop). Simply drag’n’drop images or folders into the window! You can also drop files on ImageOptim’s Dock icon.

I love the simplicity of ImageOptim, and it’s a free app.