For the month of November 2009 only, we're running a special price for personal accounts. All Ad Free, Full and Enhanced accounts are 3 years for the price of 2.
Existing users can upgrade or renew any existing account with this special price just by going to Options -> Upgrade screen and following the steps to upgrade/renew. Any existing subscription will be pro-rated toward the new subscription.
New users can also take advantage of this special by signing up a free Guest account, and then using the above steps to upgrade it.
Update: Corrected price on Ad free