Hi, yes, I am still in the stage of getting mine set up. Problem here is that one little rain barrel isn't going to water much of anything. The stored water might last about two weeks in this arid climate so people make their own out of 55 gal olive storage barrels and string them together very inexpensively. I've got ten I am planning on using.
If it rains off and on where you live in summer, one nice one will probably work great for watering your garden (bear in mind water flows down hill so you need to elevate your barrel if you plan to water something higher than it). Pre-made ones will run you between $100-$350 or you can find kits to make them yourself. I've also seen ones designed to look nicer or to have trellis with climbing vines go around them to hide them.
You might also find you fill your rain barrel after a few rains and then you will still have to divert the water coming off your roof. It probably depends on your average rainfall and the size of your roof. Alternatively, if you have the space, you can construct a dry well so that the water goes into the ground. Of course this will need to happen far enough way from the house so that it won't affect your foundation.
Here's a link with a selection of rain barrels.
http://www.rainbarrelsource.com/And some dry well information.
http://www.ehow.com/how_5039232_build-dry-wells.htmlIf you are interested in constructing your own, I can find some instructions to post as well.