The Corpus of American Historical English is a searchable index of word usage in American printed material from 1810 to 2009. Powerful complex searches allow you to trace the appearance and evolution of words and phrases and even specific grammatical constructions, see trends in frequency, and plenty more. Start with the 5-Minute Tour.
It has long been noted that style manuals and other usage advice frequently contain unintended examples of the usage they condemn. (This is sometimes referred to as Hartman's law or Muphry's law - an intentional misspelling of Murphy.) Starting from this observation, Joseph Williams' paper The Phenomenology of Error offers an examination of our selective attention to different types of grammatical and usage errors that goes beyond the descriptivism-prescriptivism debate. (alternate pdf link for "The Phenomenology of Error") [more inside]
They might actually be, you know, be useful. This year, a student in Nebraska won $1000 for finding the worst example of overuse of the phrase 'you know,' by an athlete who said it 30 times in a 135 second interview. But are they really that terrible? Known as discourse markers, phrases such as 'you know' and 'I mean' are thought to be essential in conveying information in conversation and helping us understand each other. Discourse markers also exist in many other languages and possibly even ancient languages.
If your never sure about all thing's grammatical... then this may help you. hyphens, apostrophes and split infinitives are all covered, along side many and various spellings, rules and regulations.