Rain barrels are a great way to reclaim an otherwise lost resource. This barrel can be fabricated for around $50, and will last for years. We have had a lot of luck with these barrels. I have made barrels for friends and family. We have found that we can capture and reuse multiple hundreds of gallons of rain water during a typical summer season. That means less runoff into local streams and rivers, less water around the foundation, lower water bills, and the right type of water for the right purpose. While rain water is not suitable for drinking, there's no reason to use treated municipal water on flowers and plants if rain water is readily at hand. Rain water is fine for toilet tanks and other gray water uses.
One note for those who live in cold winter climates: Remove the barrel from the downspout when chance of freezing exists. Water expands 9-10% when it changes to ice, so it will ruin a perfectly good rain barrel if it gets a chance. Be sure to empty the barrel and put it away, out of the sun, during freezing seasons.