Don't throw out those boxes!
There's someone out there who will purchase and/or take them from you. Who? Well, lot's of people. Have you seen what boxes cost these days? You can easily spend hundreds of dollars on boxes and other packing materials for even a small move. Here's a list of places to advertise your used boxes and packing supplies:
Need boxes and can't find everything you need from the classified sites listed above? You can buy great recycled boxes from Used Cardboard Boxes. They offer the same sizes and package deals as moving supply companies like U-Haul, but they are less expensive and more eco-friendly.
(Thanks to Ideal Bite for this great tip!)