It's be a bit of a faff, but Flickr will do a range of sizes with the bonus that they are then available on the 'net
More realistically I use JPEG Optimiser. I can make dramatically smaller filesizes for a given picture size. It allows you to choose a compression for the image with a 'live' look at what the result will be. It also has options to let you vary the compression across the image.
http://www.xat.com/jpegopt/index.html
Not a freebie, tho'
Then there's Irfanview. This says it's an image viewer, but it's got a lot of handy tricks up its sleeve - best to look at the "What is Irfanview" page on the website.
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