I love cardboard. It's fantastic - it's also nearly free.
Most people tend to overlook it in their day to day lives; we also tend to forget that it's made of the same material trees are made of - wood fibers. Which, if arranged properly, have tremendous physical strength, and are excellent for use as a construction material.
For this reason, I never throw my boxes away - mind you, I'm no hoarder; packing materials are broken down, sorted by type, and then stored vertically until I have a use for them. Here are just a few uses I've had for old cardboard:
Again, this is a tiny, tiny list - I've used cardboard for nearly everything. It helps save you some money, and it's pretty good for the environment too. Plus, if you can set up a stove properly, you can fairly cleanly burn it, or compost it, once you're done with it. Although, I wouldn't recommend incincerating or composting painted or contaminated cardboard.
Develop a system for storing it (don't just hoard boxes under the pretense of reuse, and stop throwing out that useful, useful cardboard!