Researchers at U. Penn have created software that generates typos. Give it a phrase, and it will generate a list of variants on that phrase, featuring things like missing letters, doubled letters, and so on. I'm not sure whether they specifically focus on typos that real people would make while typing (for example, substituting letters that are adjacent on a keyboard in a given language), but either way, I'm amused by the idea.
In addition to being cute, the code has search-relevant implications; website owners can use it to generate likely misspellings of search queries, in order to catch traffic from people who misspell their queries. I obviously don't advocate using this for black-hat SEO, but it seems to me that it has legitimate uses for white-hat SEO.