The six common Internet business models are: 1) Business-to-Consumer (B2C), where businesses sell directly to consumers, 2) Business-to-Business (B2B), businesses selling to other businesses, 3) Consumer-to-Consumer (C2C), allowing consumers to trade with each other, 4) Consumer-to-Business (C2B), where consumers offer products or services to businesses, 5) Subscription-based, 6) Freemium, offering basic services for free with paid upgrades.