September 30, 2020 updates:

Belgium ("Travelers arriving from Australia, Canada, Japan, Korea (Rep.), New Zealand, Rwanda, Thailand or Uruguay; Travelers with a consular, diplomatic, official, service or a special passport traveling on duty")
Belize (See below)
Guatemala ("aged 10 years and older" "or electronic copy of a medical certificate with a negative COVID-19 (PCR) or antigen test result issued 72 hours prior to departure")
Argentina (Newly added: see below)

Belize:
Foreign tourists must download the Belize Health App and complete the required information. Non-foreign tourists entering Belize must visit covid19.bz to follow repatriation instructions to enter the country. In addition, non-foreign tourists must also download the Belize Health App and complete the necessary information to receive a unique QR code and TRIP number which will be used upon arrival in Belize. Travelers without a negative COVID-19 PCR test taken within 72 hours of boarding can take a test at their own expense upon arrival.

Argentina:
Travelers are not allowed to enter Argentina, except for nationals and residents of Argentina. All travelers entering or departing Argentina must complete an electronic sworn statement ("Declaración Jurada Electrónica para el ingreso al Territorio Nacional") on the government of Argentina’s website within 48 hours prior to departure.

Travelers entering Argentina are subject to a mandatory quarantine for 14 days upon arrival and will have to use a COVID-19 app during that period of time. The app can be downloaded from this website: https://www.argentina.gob.ar/interio...jj-migraciones

David