XBL Diamond Program Under New Management
A trip to Xbox Live Diamond.com reveals at the top of the page that new registrations are not being accepted at this time. Clicking on the following "learn more" link reveals that the program is gearing up for a couple of changes in 2008, most notable (and only thing mentioned) a yearly fee of $6.95 to be a member of the program. So being a silver member is free, being a gold member is $50 a year, and being a DIAMOND member is $56.95 a year, although now even silver members may sign up for the Diamond program.
The site is still available to browse if you are a current member, and new members who can't wait to fork over more cash to Microsoft can do so begining on March 1.