Bonsai Wire
Bonsai wire is aluminum, and is usually anodized with a brown, dark red, or purplish coating in order to make it look like copper. It is usually sold by the kilogram, and is sized in half millimeter increments from 0.5mm to 6mm. You can use copper wire from your local hardware store, but copper has gotten expensive in the past few years, and you will find that aluminum bonsai wire costs about the same, or even a little less.
Here is a selection of wire: