You can mount the rail ($1.99) to the wall and then just clip on the colored pots that have drainage holes in them already (99 cents each). They're the perfect size for a little herb garden or a hanging plant.
Small Space Solution: Going Vertical
Best Plant Containers for Small Spaces
Round Up : Window Boxes
Herb Garden in the Alley
Inspiration : The Hanging Herb Garden
Look! Really Small Succulent Garden