Any organizing mission starts with a solid set of baskets or bins. They're perfect for linens, toys, out-of-season clothes and whatever other random stuff you have around the house, and can fit in closets, shelves or empty corners. We like this one for the top, which folds down to accommodate different amounts of stuff. It's also collapsible, which keeps it from taking up precious space when not in use. Look for covered baskets if you need to store less aesthetically pleasing contents.
To buy: Ikea, $8