If you have a washing machine that is located in your garage or along an exterior wall, that's a great place to reuse water. Typically a pipe or hose is run from the exterior wall to nearby landscaping. You can make it as simple as a hose that's moved around from time to time depending on where it's needed most. You will need to use nontoxic detergent.
Greywater Action (formerly the Greywater Guerrillas) has a very informative website with additional resources.
For more information:
To learn more about greywater systems, read Jesse Terzi's answer to a reader who asked, "We want to design a greywater system for the campground we're renovating. Can you help?"