Compare 2 Tables And Find Rows Which Don't Match (was "Mysql Noob Question")

I have a products table and a products_description table. They both have products_id as primary key. However, products_description table has more products_id keys then the products table. How do i compare the 2 tables and show just the products_id that dont match from products_descripition table?

SELECT products.products_id, products_description.products_id FROM products, products_description WHERE products.products_id != products_description.products_id;

I tried that query but got some wierd results and also the results gave me 2 columns when I just want one.