Hi 1Hacker,
Being a professor/student/employee/engineer/manager/courses instructor , we need some good PowerPoint slides/templates/animations.
In this Thread I will provide you with 3 sources which have awesome stuff 
and 
free.
1- Canva
it’s name resume all
I will redirect you to an 1Hack thread to benefit from 1 year subscription [GET] Canva Pro for one Year
2- ThePopp
It’s a Japanese website which provide you with awesome stuff 
3- SlideHunter
I just copied the site intro LoL
You can Download free PowerPoint templates and presentation backgrounds with pre-designed slide themes. Make awesome business PowerPoint presentations combining nice diagrams and graphics. Impress your audience!
That’s it
!