Xbox Live Two-Month Trial
The Xbox Live starter kit includes a two- or three-month trial card that grants full access to Xbox Live and all its content, including Netflix, matchmaking and chat. Social media services such as Twitter, Last.FM and Facebook can also be accessed with the use of this trial.
24 - 48 Hour Trial
Many AAA multiplayer games, such as "Halo" and "Gear of War," include a 24- or 48-hour Xbox Live trial card. These cards have no restrictions and allow you to access the multiplayer content of any game, including the game the card was packaged with.
Miscellaneous Trials
Select services that require an Xbox Live subscription to access, such as Hulu, may include a free Xbox Live trial when signing up for their service. The length of these trials vary, but generally last 24 hours to a week. To further entice you to sign up for Xbox Live, these miscellaneous trials will usually be extended by adding your credit card to the account.
Benefits
Xbox Live trial cards are one-time usage cards that do not require a credit card. When the time for the trial runs out, so does the gold membership. However, if you have multiple trial cards, the cards can be stacked on the same account, allowing you to keep the same Gamertag on its gold membership even longer for free or until you decide to pay for a longer subscription.