As linked to by Paul Jones there's an interesting whitepaper that's been published by Perforce Software about what they see as the Seven Pillars of Pretty Code.

The essence of pretty code is that one can infer much about the code's structure from a glance, without completely reading it. I call this "visual parsing": discerning the flow and relative importance of code from its shape. Engineering such code requires a certain amount of artifice to transform otherwise working code into working, readable code, making the extra step to leave visual cues for the user, not the compiler.

The goal of these recommendations isn't to help you structure your code better or to optimize it for the best performance. The goal is to make code that is easy to follow and simpler to read for both the experienced developers and those just coming in.

Their suggestions include making the code blend in, keeping the code "untangled", including plenty of comments and reducing clutter overall.