This link ( http://htwins.net/scale2/scale2.swf?bordercolor=white ) will take you to a cool website which gives you a scroll bar and a few pictures of things, all to scale relative to each other. You can scroll out to see bigger things, all the way as far as the observable Universe, or in to see smaller things, right up to Quantum Foam.
This would be cool enough to post all by itself, but the reason I'm posting it is because they recently updated it to include a 32,000 x 32,000 Minecraft world (just zoom out until you can see the Earth).