Last year I wrote an entry about rain barrels. If you are considering adding a rain barrel (and who wouldn't with the benifets it gives to your garden), then give this entry a read. http://gardenrainbarrel.blogspot.com/
Whether you want to collect rain water for your lawn/garden, decided to go green by reducing the strain on your city's storm drains, or just looking for another project; rain barrels might be the right option for you. Searching the web for different rain barrel systems, I found nothing that fit my situation. There are some basics to consider before you build your rain barrels: Amount of water, Filtering, Storage, and Usage.
This topic has grown a life of its own. Please visit my rain barrel blog where I go over this topic and explain why I chose my rain barrel design.