OK, I'm sure it's not really an innovation, but it was the first time I'd ever seen it, and it makes so much sense! I just finished reading The myths of Innovation, by Scott Berkun, and instead of offering the standard semi-useful bibliography, at the end of this book he provides a ranked bibliography. The bibliography shows the books from which he took the most notes first. What a great idea!
It's a really quick read, only 150 pages of actual text, and it did a really good job of sparking some ideas as I was reading. The colophon is not to be missed either ;-)