Oh man. I'm tempted to just sit back and let you marvel at the beauty, history, innovation, and intelligence that is on display in the picture above, taken and posted by Robert Donovan on Flickr (and be sure to check out the alternate view, too -- I actually like the alt view better, given that it shows all of the ports over time). But just in case you're wondering:
Unibody 13" 2.53Ghz Intel Core 2 Duo MacBook Pro
15" 400Mhz G4 Titanium PowerBook
15" 1.25Ghz G4 Aluminum PowerBook
15" 2.5Ghz Intel Core 2 Duo MacBook Pro
Amazing stuff -- think of the engineering, manufacturing work, and design arguments that went into those little bands of metal, and all of the good work and art that has since been created with them. Beautiful.