A good resource is here:
http://www.forodrim.org/daeron/md_hmch.html#sixties
The latest writings, in chronological order, are:
- A Description of the Island of Númenor
- Aldarion and Erendis
- The Palantíri
- The Line of Elros: Kings of Númenor
- The Shibboleth of Fëanor
- The Problem of Ros
- The Disaster of the Gladden Fields
- Cirion and Eorl
- The Battles of the Fords of Isen
- Of Dwarves and Men
- The History of Galadriel and Celeborn
- The Drúedain
- The bunch of texts titled "Last Writings" in HoME 12.
The bulk of these - from The Shibboleth of Fëanor onwards - are dated to 1968 onwards, with those from The Disaster of the Gladden Fields onwards being dated to 1969 onwards.
In addition to these, there are a number of other works such as the writings associated with the 2nd edition LotR and 3rd Edition Hobbit (which were both much later in Tolkien's life than may seem to be the case), as well as the abandoned 1960s rewriting of the Hobbit itself.