Image Resizers is an interesting app with a two-pronged approach to shrinking JPEGs,PNG,GIF and so on. First, it uses a smart algorithm to figure out how much an image can be compressed without visible effects (so the program isn't lossless, but it's not just re-encoding at some fixed quality setting, too). And then the program uses its own image encoder to try and deliver the most compact files possible.
There's plenty going on in the background, but none of this is visible to the user. Just drag and drop your pictures onto the program and it'll replace the originals with compressed versions.
The results here can vary greatly, when we presented the program with 25 large digital photos they dropped by 85 percent to 94 percent and with little obvious quality loss.
Image Resizers doesn't do anything too amazing. The compression possibilities ramp up considerably as your images get larger. If your graphics are on the bulky side then it's definitely worth giving the program a trial to see how it works for you.