More to explore:
DIY plug in air fresheners.
How to refill Wallflowers with essential oils. Awesome tutorial, less awesome woo in the blog entry.
DIY Wallflower refills. (This may not be cheaper than buying Wallflowers, because it depends upon how much the essential oils cost and how long they last. I will have to do some research on that.)
reuse bath body works wallflowers ... holy cow do we have a zillion of these in a bag in the closet!
Wallflowers Refill DIY - use Essential Oils