You can use photoshope to optamiz your graphics, many GIFs look just as good with fewer colors, and many JPEGs look just as good with a higher compression level.
Save for Web & Devices in Photoshop/Illustrator.You can use the optimization features in the Save For Web & Devices dialog box to preview optimized images in different file formats and with different file attributes. You can view multiple versions of an image simultaneously and modify optimization settings as you preview the image to select the best combination of settings for your needs. You can also specify transparency and matting, select options to control dithering, and resize the image to specified pixel dimensions or a specified percentage of the original size.
When you save an optimized file using the Save For Web & Devices command, you can choose to generate an HTML file for the image. This file contains all the necessary information to display your image in a web browser.
NetMechanic also offers an image optimizer program online.
You should also analyze the HTML of your site. Make sure you use relative paths, so that images are not downloaded more than one time. Remove any extra spacing and when linking to other pages, use relative paths and not absolute links.
While many hosts already have it, you could also see if your host has mod_gzip installed. This can save you a lot of bandwidth.
Best of all, optimizing your page like this makes the user experience better as your site will load faster for them!