Many objects can be repurposed as useful and attractive planters (even Styrofoam packing materials), but using wine crates for planters feels functionally and aesthetically right to me. Fortunately, all you need to do to convert a wine planter is drill holes for drainage, seal the wood from the elements and fill with soil.
After drilling several one-inch (2.5cm) spaced holes on the bottom of the crate, Apartment Therapy weblog recommends using a few coats of Thompson's Waterseal so that the wood will develop a natural grey patina over time. Now you're almost ready to fill the crate with soil, but you may want to apply a layer of river rocks, gravel, or even Styrofoam packing peanuts to further improve drainage. After that, add your soil and you're ready to plant.
One of the great things about using a wine crate as a planter is that they're small enough to start plants inside and then bring out after the last chance of frost. This allows you to get a few extra weeks of growing time for any plant that can thrive in shallow soil.
How To: Create a Repurposed Wine Crate Planter [Apartment Therapy]