Preheat oven to 350F. Cream together peanut butter and sugar. Beat in eggs one at a time. Add baking soda and vanilla, stir until combined.
Roll into one inch balls and place two inches apart on a baking sheet. Flatten with a fork to get the criss cross pattern, and bake for 8-10 minutes. Allow to cool on baking sheet for a few minutes, then transfer to cooling rack.
Alternatively, bake as balls and press a chocolate kiss into the top immediately after removing from the oven. You can also mix in nuts or chocolate pieces for tasty variations!