We just moved into a 4-bedroom house and still have about 60 boxes for sale (small, medium, large and extra-large moving boxes, already flattened). I already sold the boxes from the standard sizes (below), and the boxes I have left are approximately the sizes below.
Medium Moving Box $1.00/each --- 18" x 18" x 16" (W x L x H)
http://www.uhaul.com/MovingSupplies/Boxes/Standard-sized-moving-boxes/Medium-Moving-Box?id=2793
Large Moving Box $1.25/each ---- 18" x 18" x 24" (W x L x H)
http://www.uhaul.com/MovingSupplies/Boxes/Standard-sized-moving-boxes/Large-Moving-Box?id=2753
Extra Large Moving Box $1.75/each --- 24" x 18" x 24" (W x L x H)
http://www.uhaul.com/MovingSupplies/Boxes/Standard-sized-moving-boxes/Extra-Large-Moving-Box?id=3588
Some of the boxes were used for shipping, but they are still in excellent condition. All boxes have been flattened.
I also have 10 large boxes, with bubble wrap, packaging paper and/or Peanuts. $5 each