ThinkGeek offers the Green Lantern Insignia Ring for $14.99 plus around $6 for shipping. That's $15 off and the lowest total price we could find. While this ring does not grant control over the physical world, it also doesn't require recharging every 24 hours or discriminate against wooden objects. It's available in sizes from 8 to 14.
The Microsoft founder -- and richest man in the world -- also suggests one great book to read.