The "is" of simple predication:
Obama is a US citizen.
The "is" of (Clintonian) existential predication:
There is no affair.
The "is" of moral judgment:
War is evil.
The "is" of artistic identification:
That upside-down tree is a work of art.
See also Sherri Irvin's critical commentary on Danto's "is of artistic identification/constitution."