E pluribus unum ("out of many, one") had been the unofficial motto of the United States of America from it's inclusion on the great seal in 1872. The motto, which originally stood for many states coming together to form the nation, but has since come to represent the idea that out of so much diversity a single unique and distinctive american people have emerged. The motto continues to be used on currency, in our great seals, and elsewhere.
Officially, the current motto of the United States is "In God We trust", selected by congress in 1956. However, there is no stipulation that we may have only one national motto.
Therefore, in regards to it's history and usage past and present, I propose that "E pluribus unum" be set as the second official motto of the United States of America.