A few weeks ago I picked up this nifty wall storage set at ikea. After hanging the tallest bin above the counter for mail as I'd planned, I realized the short ones would be perfect inside cabinet doors. The hinges on our cabinets help create a bit of extra space when the door is shut, so the bins actually take up very little room inside the cabinet.
So, I ran back to the store to grab smaller quarter inch screws (to avoid having them poke out the front) and another set of bins, because I suddenly felt like putting them in every cabinet of the house... I came to my senses and settled on two in the spice cabinet, one under the kitchen sink, and two under the bathroom sink. They're easy to install, and because the bins rest on a rack, you can easily remove them to clean or rearrange contents. I'd definitely recommend them! Although now every time I open the cabinets, I totally geek out.