Today is the day, Hogwarts students! OWL/NEWT scores, admission letters, and supply letters have been sent out! Of course, some students will receive a little something extra with their post this year...

Gryffindor Prefects: [NPC/TBD] and Greta Gillenwater
Hufflepuff Prefects: [NPC/TBD] and [NPC/TBD]
Ravenclaw Prefects: Cadogan Glynn and Millie Potts
Slytherin Prefects: [NPC/TBD] and Violetta DeCroix
Quidditch Captains: James Fletcher Abraxas Crabbe Nicodemus Dursley Sirius Black
Head Students: Sirius Black and Flora Mulciber

Note: This information is not "public"—your character will not immediately know who earned what titles until they learn through the grape vine. The exception is Hogwarts staff, who would have received a note with the list of new prefects and the head boy/girl :)

In addition, Benedict Hunter has been retconned in as a prefect in Gryffindor House.