A mold, something the right circumference. A soda can could work, or any bottle. I used a bank-thing I had lying around.
Wire, obviously. It should be something you can tell is sturdy enough not to bend when you've actually made the bangle, but flexible enough to shape. You could use any color.
Pliers and a wire cutter. A wire cutter especially.
A soldering iron and solder: Only if the wire you have is solder-able. Mine wasn't, so I just used hot glue.
Nail polish the color of your wire.
A hot glue gun. This is very important.
Music to make bangles to. Zombie Nations
happens to be very good bangle-making music. Music is optional, but recommended. Cutting and gluing wires gets tedious.