Sorry, this page is Very Much IN PROGRESS! The main idea so far is, unless they specifically ask for something, include only the cover letter! It used to be common to include a photo; these days, that is considered not merely old-fashioned but vain, and can subject you to being roundfiled for giving away your race too early (no matter what your race is).
It is common to ask for salary history. Some people say don't give it even if asked; I say, give 'em what they ask for or they'll roundfile you right off; they'll ask it again on their application anyway.
It's also common to ask for writing samples. Sometimes this is just to see how well you communicate by writing. Some, however, demand a handwriting sample, for personality analysis. I say, any company that does that, is a bunch of kooks that I wouldn't want to work for.
In programming, it's also somewhat common to ask for code samples. This is so they can check out your coding style. Pick a page or so of your best, cleanest, most elegant (not most obscure!) code.