Ebates, the popular cash back shopping portal, is running a Cyber Monday 600 special today only. Get double cashback at over 600 stores when you click through their portal. If you’re not familiar with shopping portals, you can read my full primer here. In short, shopping portals are websites that provide links to various retailers’ websites. In return for directing customers to their site, those retailers pay a commission to the portal for each customer that makes a qualifying purchase. The portal then allots a portion of that commission–in the form of points or cash–to the original customer. For example, today only you can get 12% cashback at Macy’s and 10% at Bloomingdales. Check your…