Reposting from DDMS
Other destinations open / opening to US travelers from some research:
St. Lucia – Open. A negative test is required for entry.
Antigua and Barbuda – Open. Temp. checks and face coverings mandatory until September. No quarantine requirement.
Jamaica – Open
Bahamas – Opens July 1.
Aruba – Opens for Americans July 10.
Puerto Rico – Opens July 15
Turks and Caicos – Opens July 22
Tanzania – Open
Maldives – Opening July 15
French Polynesia / Bora Bora – Opening July 15. Will require negative test result within 3 days of travel, or proof of antibodies.
Sri Lanka – Opens Aug. 1. A negative test and minimum 5-night stay is required.
Cancun and Cabo in Mexico are open I believe.