I have often wondered how ZIP codes were laid out across the US -- what's the logic behind my Portland, Oregon address having a ZIP starting in 9, while New York addresses start with 1?
Well, the web has tons of resources to help you figure out ZIP codes. First is Ben Fry's zipdecode, an interactive web site that lets you type in a ZIP code and watch the map narrow down as it searches for that code. (Try it -- it's neat and educational.) You can also use this interactive map to see the logic in the nationwide layout of ZIP codes -- start by typing a 0, then backspace, and type 1, and so on...up through 9, you'll see the ZIP codes laid out from northeast to the west. Also check out Robert Kosara's US ZIPScribble Map, which connects the various numbered zones via colored scribbles. (Thanks to Geo Lounge for these pointers.)
And finally, here are some ZIP codes I found interesting: