#764
"Fly the British Airways Concorde eastbound from New York to London; return in coach class on regular aircraft"
200,000 points
The fine print states "Economy travel to New York is provided on one flight segment from any city in the contiguous 48 U.S. served by Delta, TWA, United or US Airways."
Although the blackout dates have not been updated for 2001-2002, they appear to be (approximately) January 1-7, Easter week and December 17-24.
Above info is per pages 20 and 39 of the 1998 Guide to Marriott Rewards
This award is presumably still valid for a request through July 31, since there are no indicated changes to the award in either the 1999 or 2000 updates.