So both of my credit cards are linked to my Amazon account so that I can apply my reward points toward Amazon purchases. Unfortunately, these points do not apply to e-book purchases.
However, a few minutes ago, I discovered they can be used to buy Amazon gift cards. So I bought myself an Amazon gift card with my reward points and now I'm splurging on e-books.
Everyone else in the world may have already known this but I thought I'd pass it along.