I use 30 gallon Rubbermaid garbage cans and simply divert the downspout into an opening in the lid, making sure I attach a nylon stocking to the end of the downspout to keep bugs and stray wee leaves out. Nice thing about the Rubbermaid garbage cans is they are so dang easy to clean twice a year and last years and years, even in our heat in summer and cold in winter. You must have some type of screen or nylon sock set up because you do not want mosquitos laying eggs in the water. And with a male female hook up at the bottom you can attach one can after the other so when it rains they all fill up well.
i made my own last summer i took a plastic barrel with 2 spouts at the top cut a hole in the bottom big enought for the down spout to drain in added a shower drain without the metal piece, the barrell will be up side down put a spigot i one of the holes added a pvc connector inside to keep the spigot in place attached a short hose pipe to the spigot. i elevated the barrell with cement blocks workes fine.
You can see how to on an episode of Renovation Nation. Which episode I'm not sure. They just added a faucet close to the bottom of the barrel so you can turn it on or off or add a water hose. It was so easy looking and neat. Sorry I don't have a link. I'll see if I can find it for you. Good Luck!
...When one flower blooms,spring awakens everywhere.... - John O'Donohue
Thanks so much for the idea and link. Can't wait to set one up soon. I don't think I have ever seen a real rain barrel. I've just sang about one over and over in the playmate song. It will be so fun and useful to actually have one.