Here are some resources I used for creating these free Keynote templates.
Do you need PPT files (for Windows users) instead of Apple keynote (Mac users)? Try best powerpoint templates website – many free powerpoint files there.
Recently I found FreePik, which looks very promising. Use vector elements from FreePik website in your designs to make your presentations extra special.
And finally, I suggest a consistent color theme in any keynote presentation that you create. I used this great free color theme generator.