Growing up, we'd douse cotton balls in peppermint oil and drop them in corners or under furniture to help keep the mice - and some insects - away. It won't kill them, but they find it very irritating and will avoid the area if they can.

This is not a great idea if you have pets, mostly because they'll either try to eat the cotton balls or get annoyed by the smell. But as a bonus for you, your house will smell minty fresh!