Animal Essential's Hairball Relief is fantastic for hairballs. It is a liquid tincture made from 100% Organic Marshmallow root and vegetable glycerin.
Cats: 0.5ml to 1ml 2 to 3 times daily
under 20 pounds: 0.5ml to 1ml 2 to 3 times daily
20-40 pounds 1ml to 1.5ml 2 to 3 times daily
over 40 pounds 2ml 2 to 3 times daily