The words you will see below contain the doubling rule.
In most cases, when adding an ending or suffix to a one syllable word that ends in with vowel/consonant combination, you double that consonant. For example: mad/madder
If a one syllable word ends with a vowel/consonant combination, you should double the final consonant if you are adding an ending that begins with a vowel such as: -ing, -ed, -er, -est, -en, -y, -ish. For Example: top/topping
Here are five lists that include the doubling rule:
Doubling Word List