I dug a little deeper than necessary in solving a problem over at rosalind.info and ran across this excellent essay explaining a fast method for finding the longest common substring, a not-uncommon problem in bioinformatics. The other half of my joy came in finding Ilya Stepanov already wrote a version in python [1].
[1]: https://gist.github.com/istepanov/6506508#file-lcs-py