Since I live in a second floor condo apartment, gardens aren't an option for me. However I do live in a county that puts much effort into encouraging this sort of thing, and this is what they say on their website.

http://environment.arlingtonva.us/st.../rain-gardens/

Also note the links under "Resources" on the right side of the page.

They also have a page on rain barrels, also with Resource links.

http://environment.arlingtonva.us/st.../rain-barrels/

Good luck!