"Don't fire until you see the whites of their eyes" has been attributed both to Prescott and to Israel Putnam. Apparently the earliest source for it is something written by Parson Weems (of the George Washington cherry tree story) decades later. The accounts written shortly after the battle do not quote the line. Prescott was in command at the redoubt and was insistent on his soldiers not firing before they were ordered to (because their ammunition was woefully insufficient--that's why they were finally driven out during the third British attack), but he may have used some other expression to get across his point.
The most serious loss on the American side was the death of Dr. Joseph Warren, one of the most important Patriot leaders in Massachusetts.
Prescott, Arizona, is named for Col. Prescott's grandson, who was a famous historian.