If you think that artists should work for free because your project will give them great exposure (and anyway, art isn't really work, because people like to do it) then stay away from Ryan Estrada's latest Twitter account, For Exposure, which mocks that attitude by posting real requests from the Internet. On the other hand, if you believe in paying people for their work and you need a good laugh, check it out. The tweeted material is presumably from aspiring comics writers, although they might think about paying an editor, as misspellings and grammatical errors are legion.
For good measure, he also presents a dramatic reading (below) of a letter requesting an artist work for free — actually, offering it as if it were a great opportunity.
Of course, Estrada himself offers a number of his comics for free (highly recommended: Aki Alliance), but that's his choice and, no doubt, part of a business plan that's more solid than "Maybe someday someone will pick this up for a movie."
Anyway, as Gary Tyrrell (from whom I got this link) observes, people die of exposure.