For an easy-to-follow guide to rain gardens, check out the WSU Extension's Rain Garden Handbook for Western Washington Homeowners.
WSU has more in-depth information on rain gardens on their website.
How-to guide for caring for your rain garden. Rain Garden Care Guide.
Ecology created a Rainwater Harvesting Calculator (RWH) to help Washingtonians size their RWH system based on the typical climate where you live.