With credit to Valerie Neal, here is the list per a May 26, 1978 memo from the Associate Administrator for Space Transportation Systems (John Yardley) to the Director, Public Affairs on the subject: Recommended Orbiter Names.
Recommendations by an ad hoc committee on names for Space Shuttle Orbiters; chose "names having significant relationship to the heritage of the United States or to the Shuttle's mission of exploration."
Recommended List of Orbiter Names
(In descending order of preference)
Constitution
Independence
America
Constellation
Enterprise [reserved for possible 5th orbiter, to carry on OV-101's name]
Discoverer
Endeavour
Liberty
Freedom
Eagle
Kitty Hawk
Pathfinder
Adventurer
Prospector
Peace