We've offered several IKEA kitty litter storage hacks in the past -- there's something about cheap Swedish-designed furniture that just seems to inspire cat owners. The latest we've encountered requires a bit of DIY nous, but the result is impressive.
At IKEA Hacker, Ben outlines how he built a combined kitty litter and cat food cupboard from the IKEA PS cabinet, with an underneath entry so that the cat doesn't have its food stolen by the resident dog. The metal structure means you've got a sturdy environment, but you have to be handy with a metal saw. Some cats might also draw the line at such a relatively awkward entry, but for the average box-loving feline it's unlikely to be a problem.
Ikea PS locker into litter box [IKEA Hacker]