Anywhere cool & dry, and rodent free. Basement in rubbermaid tubs and/or food-grade buckets is great. I just keep it in it's original bag in a rubbermaid tub.
Do you have a local homebrew shop? That's where I get mine. Prices aren't as good as Williams, etc, but no shipping. And still far better than buying by the pound.
Edit: See this thread for storage: