A more convenient image-smushing tool?

Yahoo’s SmushIt is a nice tool, but I don’t find it very convenient to use. You have to go to a site, upload the file you want, process it, then re-download and manually overwrite the original file. Then, if you decide to change the file later, you’ve go to do the whole dance again. I realize that Firebug integration with ySlow makes this a little easier, but what I really want is a non-hosted tool - something that runs on my computer to where I can right-click an image, or a set of images, click “Smush these images” and be done with it. Anybody know of one?