This video gives great step by step instructions on how to build a garden tower out of a food grade barrel. These garden barrels are a great re-use of what would otherwise be a land fill nightmare. They also serve to maximize use of space and could be a significant for square foot challenged gardeners.
One of the best uses I have seen for this design is as a means of growing strawberries, but they would do well with a large variety of herbs, flowers, greens or any other smaller plant.
As a bonus, this particular design utilizes a built in worm composter so your plants can have access to the castings that only a good vermicompost system can provide.
Enjoy, and then go grow something.