Serious Stuff:
Renewable Energy (ethanol, solar) projects
Building electronics devices
Investing and finance
Car repair and maintenance
Just For Fun:
Flying model RC airplanes with the kids
Skiing and sledding
Hiking in the mountains
Cooking and experimenting with recipes
Fishing
Travel
Digital photography
Visiting bookstores
Playing the piano
Playing chess
Tabletop water fountains
Interior and exterior lighting
Admiring good architectural design