President Bush will host a luncheon for President-elect Obama at the White House on January 7, 2009. In attendance will be all of the former living presidents: Jimmy Carter, George H.W. Bush, and Bill Clinton.
This is the first time an event of this sort has taken place. There have been rare events where all of the former living presidents at the time have been together (another president's funeral, presidential library openings, foreign missions), but never before have they all got together in honor of a newly elected president who has yet to take office.
It will be interesting to see if this becomes tradition during transitions of the future.