4. Gucci Mane, Buy My Album (2010)
Successful rappers don't release free mixtapes for fun-they do it to drive sales for their real, pay-for-play albums (and tours, merch, etc.). So we've got to give Gucci points for blunt honesty: He dropped Buy My Album just five days before the release of his third studio album, The Appeal: Georgia's Most Wanted.
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