This works for me because:
1) I live alone, so ALL YOUR PEANUT BUTTERS ARE BELONG TO
2) I mostly use peanut butter to make no-bake cookies anyway.
So, how I get the last little bit of peanut butter out of the jar:
Sprinkle small amounts of quick oats into the jar.
Stir it around until the peanut butter left at the bottom is fully soaked up by the quick oats. This will also scrape the last little bits off the sides. If the oats look greasy or are sticking together, add more.
Add sugar to taste.
Dump in bowl. Add anything else you may want (chocolate chips, raisins, coconut flakes).
Nom with spoon.