Possible Clues:

• Monument in Washington D.C.
• Backing for some U.S. currency?
• Landmark dedicated on 5/30/1922
• Backdrop for the 'I Have a Dream' speech
• Shrine near the National Mall
• U.S. cent depiction, 1959-2008
• Building on a fiver
• Site of the 50 Across speech
• Washington monument
• Half dying to tuck into green food? That's a landmark for Americans!