Wizards of the Coast is providing free Magic: The Gathering cards to new players. All you have to do is invite a friend to play.
Existing Magic: The Gathering players who want to get one of their friends in on the action can do so by logging into their Wizards account and snag their referral link to send to a friend. That friend can then click through the link and WotC will send them a free Welcome Deck.
Welcome decks are ready to play right out of the box and include two 30-card decks (one of the indicated color and one randomly inserted of one of the five colors of Magic). The decks can then be played as-is, or combined Jumpstart-style to make for a traditional 60-card deck. Do note, though, that Welcome Decks are not Standard legal as they contain cards from across Magic's history.
Wizards of the Coast says that this refer-a-friend Welcome Deck promotion is available in the U.S.A. only and only while supplies last.