WP Smush.it is a WordPress plugin by alexdunae that reduces image file sizes and improve performance using the Smush.it API within WordPress.
stripping meta data from JPEGs
optimizing JPEG compression
converting certain GIFs to indexed PNGs
stripping the un-used colours from indexed images
Smush.it offers an API that performs these optimizations (except for stripping JPEG meta data) automatically, and this plugin seamlessly integrates Smush.it with WordPress.
How does it work?
Every image you add to a page or post will be automatically run through Smush.it behind the scenes. You don’t have to do anything different.
You can also run your existing images through Smush.it via the WordPress Media Library. Click on the Smush.it now! link for any image you’d like to smush.
Download and info: http://wordpress.org/extend/plugins/wp-smushit/