I was just web-surfing one evening, in a non-teleological way, when I found this article (Minty Water Valve Controller « RAYSHOBBY.NET). It is now a commercial product that can be bought complete or in kit form. If you keep cruising through the blog, you can read about the origins of the project, suggested parts, and Eagle schematics. This page of the blog (Update on ‘How to control Orbit 62035 valve’ « RAYSHOBBY.NET) displays an updated version of the controller circuit, and a downloadable schematic. It's amazing what you can find on the Web. I think that I was looking at Arduino boards and shields, which lead me to SparkFun, which lead me to the up-coming Maker Fair, which led me to....