In the woodworking world box joints are my favorite looking joint. I like simple lines and box joints are nothing but simple lines. Box joints are very easy to create in SketchUp.
You can make a box joint by drawing out each individual finger in model space before you push pull the area into a 3D shape. You can also cut out the fingers after the 3D shape is created. After you make one side of the box joint the rest is super easy. Check out the video for a visual guide showing how easy box joints are to make in SketchUp.