Shelves are obviously a great idea as you can stack them in lots of different ways, put dividers in to make 'mini shelves' and display things in really interesting ways. But you could also use them to plant herbs in, as draws or even make kitchen unit doors from them.
I know you can buy wine crates online but they're fairly expensive and I never want to buy things like this that can be collected for free. The ones I have were found stacked outside someones house waiting for the bin man!!