Microsoft posted the official announcement of the new Xbox Live pricing and package. It matches the info leaked last week:

"Microsoft today announced that the next generation of online multiplayer gaming service Xbox Live will be available in North America on the Xbox 360 video game and entertainment system starting this holiday. In addition to the free Xbox Live Silver membership available to every Xbox 360 owner, for only $49.99 (U.S.) gamers can amplify their gaming experience with a 12-month Xbox Live Gold membership. Gamers looking for a truly engaging and immersive online multiplayer experience can pick up one of the Xbox Live Premium Gold Packs, which include the new Xbox 360 Headset, Xbox Live Arcade games, Microsoft Points for use in Xbox Live Marketplace, and mail-in rebates for up to $20 (U.S.) off any Xbox 360 game.

Microsoft also today announced that credit cards will no longer be required to create an account on Xbox Live for Xbox 360, removing one of the biggest barriers to entry. Gamers can purchase 12-month Xbox Live subscription cards via cash or other payment methods at any participating retail store. Subscriptions will also be available for purchase by credit card in one-month, three-month, and 12-month increments through the Xbox Live Dashboard.
The next generation of Xbox Live will be offered to gamers through two levels of service. Xbox Live Silver is a free level of the service offered to all who own an Xbox 360 system, a high-speed Internet connection, and a memory unit or a hard drive. The Xbox Live Gold membership delivers the full Xbox Live premium online experience annually for $49.99 (U.S.)* which averages to a little more than $4 a month (U.S.). The Xbox Live offers include the following:
* Xbox Live Silver membership
This free level of service lets members connect to the online community and create their own digital identity with an Xbox Live gamertag and personalized gamer profile. Xbox Live Silver members will be able to send and receive text and voice messages and join their friends on Xbox Live. Xbox Live Marketplace is the one-stop download center for additional game-related content like free trailers and demos as well as content that adds more to games, such as new levels, characters, and weapons. Gamers can also purchase and download fun, casual, and highly addictive Xbox Live Arcade games directly to their Xbox 360 system (additional fees may apply; hard drive or memory unit required for downloads).
* Xbox Live Gold membership
This includes all Xbox Live Silver-level features and access to premium multiplayer experiences exclusive to Xbox Live Gold members. This includes online multiplayer gaming, enhanced matchmaking and feedback tools, and exclusive privileges and rewards on Xbox Live Marketplace."