Longtime Republican Senator Pete Domenici is retiring and not seeking reelection. So far both the First District Representative, Heather Wilson, and the Second District Representative, Steve Pearce, are running for the Republican Nomination so are not running for reelection to their seats. Reports are coming out that Third District Representative, Tom Udall, will seek the Democratic Nomination -- which is also being sought by Albuquerque Mayor Martin Chavez, but not by Governor Bill Richardson who is still trying to get the Democratic nomination as President.
Thus, all three congressional districts, and the senate seat up for reelection, will be served by new people starting in early 2009.
I don't know enough electoral history to know if any state has seen this level of new representation in Washington since statehood or not. Of course this can only happen to the smaller states, since there is no way a state with a large number of House Seats could possibly have every representative run for a vacant Senate seat or other office.