These are all great replies, guys!
I just found out about this chain of websites run by a company called 'Envato'. I've signed up for their 'Envato Marketplaces', and even though they require an over-18 person, I have parental consent to join, and Envato knows this and are fine with it.
Basically you sell your works. For example, you can sell WordPress themes or just themes in general at ThemeForest. You can sell code snippets or full-blown webapps at CodeCanyon. Graphics and the like at GraphicsRiver. You don't make a lot off of each purchase, usually around $5, and you get to keep %50-70 of your earnings, but I think it's a good deal, considering you can sell your useless code and unused themes for nice low prices.