According to Major Nelson’s blog, the price has been the same since 2002 and hints that the expanded services Microsoft is adding to Xbox LIVE is the reason for the price increase. Recent additions to the service include: avatars, facebook, twitter, last.fm, Zune video and Netflix. The service will also be upgraded soon to include: ESPN 3, Kinect and Zune music. As stated elsewhere, with Kinect coming soon and the rush of new users likely to sign up for the service, it seems that this is an ideal time for the price increase.
Here is the pricing chart with the new gold plan costs coming soon:
To help current gold subscribers keep the cost down, Microsoft is providing a way to lock in their subscription for the next 12 months at the current price. If you wish to lock in the discount, visit here.