Ask your local dairy if it can use your milk crates. People often steal milk crates from dairies--often to feed the black market for recycled plastic--and the loss drives up operating costs, which are passed along to consumers in the form of higher prices.
Sell the crates or offer them for free to your neighborhood grocery and convenience stores. They can use them to carry heavy products like meats and soda bottles and to keep their stock rooms organized.
Use the milk crates for storage. Since they can withstand harsh environments and dampness, milk crates are great for storing items that are exposed to the elements and fluctuating temperatures. You can keep them in your basement, attic, garage and outdoor shed as well as inside your house.
Make furniture out of your milk crates. College students have long used milk crates to construct makeshift shelves and preserve vinyl albums so they don't warp. Crates can be turned into chairs, tables and beds, primarily just by stacking them next to or on top of one other.
Turn milk crates into artwork. There are artists who specialize in making art out of milk crates; you can locate them by running an ad in your newspaper offering to donate materials to them. Or you can use the crates yourself to make sculptures or hanging artwork.