Here is a list of a few other tools within Photoshop 5.5 or Image Ready 2.0 that are of value to webdesigners:
Slicing a Page - Image Ready allows you to divide an image into slices so that each section of the image can be dealt with seperately. It is a little like creating an image map in that you can make each slice a seperate link.
Creating Styles - Image Ready has some built in image styles(woodtone, ice, etc.) that you can apply to an image or layer. You can also create your own style and save it for later use. This last feature is useful if you create an image style that you want to use over and over again.
Art History Brush - Turn a photograph into a work of painted art. If you want to funky up a photo, experiment with this tool in Photoshop.
Multiple Image Layouts - Photoshop 5.5 will create a page of thumbnail images for any folder of images you have. It will even create the HTML document(but that's cheating, isn't it??) that holds the clickable thumbnails.
Typing Tool - It's not really new, but much improved in Photoshop 5.5/Image Ready 2.0. Make sure that you have "anti-aliasing" turned on when you create type for the web. It smooths the edges.
If you are interested in trying any of the above features, use the Help menu in Photoshop or Image Ready. There are also multiple, multiple online tutorials on Photoshop. Search away.