Here's a presentation slide I've been meaning to put together for a while. It shows the major moons of the eight planets, to scale with each other. Below is a labeled version. You can download one without text here, and if you scroll down I've got a couple of alternative layouts.

Note: it's been pointed out to me that the Callisto image is from Voyager, not Galileo. I'll fix the text on the image eventually. --ESL