CSS Image optimization

Image optimization, plays a majore role inorder to load your page faster. There are many good image editing tools that allow us to get the best visual result for a certain file size, but they lack in quality. Saving bytes has never been so easy. Smushit! is a service that goes beyond the limitations of Photoshop, Fireworks & Co. It uses image format specific non-lossy image optimization tools to squeeze the last bytes out of your images - without changing their look or visual quality. This tool now is also recommended by YAHOO and GOOGLE.

How it Works
You can give any format image like gif, jpeg or even png. Smushit will convert your given format file into png8 format. PNG true colors such as png24 will not support by ie6, but png8 will be supported by all leading browsers.

I also recommend this. for more optimization info also visit Page Speed by google