Sawastea is right, Fish oil is probably the best, but Flax oil is a close second. Flax is much cheaper too!
Basically you want to look for sources that are high in monounsaturated fats (also known as EFA's…Omega-6 & Omega-3). Because most of the EFA's we all eat come from predominately Omega-6’s, the very best fats are those with a high ratio of Omega-3's to Omega-6's. That basically comes down to Fish and Flax oils.