I've uploaded plans for a rain barrel that the Texas Coop Extension has distributed. It's very to easy to make. I'll attach photos later of ones someone made this year. What I like about these is that you do not have to place them under the down spout on the roof. Instead,you can place them where you get the most water.
Also, here are a couple of links for a few plans to make Rain Barrels. The one from Lowes even has a video included.
How To Make A Rainbarrel
Water-Conserving Rain Barrels
I'm adding to this post on 9/26/09
I've finally had a chance to add some photos to the rain barrels that were made. One has a faucet, the other does not. Both were made off the same basic plan from the Texas Coop.
This last image I'm including to show where we placed the rain barrels. One is under the spout. We originally had it elsewhere, but because of the lid, was not able to get much water.
The other barrel is next to it, collecting run off from the roof that misses the gutter.