You can pick up a galvanized metal tub at the hardware store. This tub is a fairly shallow oval shape, which works well grouped with other containers. The only caveat with metal is that if you live in a hot climate you need to be careful or you'll cook your plants. To prevent this, either keep the container in the shade or line it with bubble wrap or something else with insulating properties. I also line all my metal containers with plastic because metals can react badly with some plants.