Renting online from Blockbuster and having an actual in-store account are different. To sign up for a membership, you need a valid driver's license and a valid credit card (or a debit card that's Visa/MC/Amex/Discover). The reason Blockbuster asks for a credit card is in the event you have movies that are waaaaay late (like over two weeks...it varies from store to store) and your credit card gets charged for the movie. Hopefully that never has to happen, but that's just store policy. And Blockbuster doesn't share your credit card with other third market parties (we're not SUPPOSED to, or else we'd get in major trouble).

If you don't want to use your credit card, you can always use your car registration or a recent paycheck stub as a secondary form of ID.