Scrapbook paper (or any type of decorative paper)
Measure along the front; make a mark and use your scissors or exacto knife to cut along the line. We didn't cut it completely off however. We scored it and pushed the flap inside and into the bottom to make the bottom better reinforced. Make sure you leave enough height so whatever you place inside will not fall out too easily.
We cut the sides but at an angle to give it a better, more sophisticated look. Also, it'll support the back better. We also cut off the top and side tabs.
Then, take your scrapbook paper and glue and get to work! It took a lot of measuring and cutting to make sure the pieces were the right size and would fit. We even glued some pieces on the inside of the side flaps so you can't tell it's just a box. We were able to cover the box with just two pieces of scrapbook paper.
Of course I had to test this right away. It went straight up on the wall and I cleaned all the mail off the table. It looks so much better and you can't even tell the organizer came from a cereal box! This practically cost nothing to make as we had all the supplies on hand. The good news is, next time I finish a box of cereal I can make another. I'm pretty sure we will too!