I frequently use portals to do my online shopping to either earn cashback or airline mile. The Frequent Miler rights a blog about unusual ways to earn cash back or airline miles/points. Currently, the Frequest Miler is recommending CashBackMonitor.
CashBackMonitor will show you the highest earn rate at any particlar store you wish to shop at. One of these shopping portals that offers cash back is called Ebates. Currently if two of my readers sign up for Ebates through my link I will receive $50. I will definately put this $50 back into the blog in order to help develop content!