If you want to make some hanging shadow boxes, then you need to consider the best types of wood for this project. Different types of wood can have an effect upon the impact which your shadow boxes make, and this can also effect the appearance of the objects inside your box.
If you want to create a feature where the box itself is only a background feature to the object, or if you have very dark objects which need a light background to show them off properly, then you should build your shadow boxes using a light balsa wood. These woods need to be thick enough to support the weight of the object, so opt for something which is at least 4 or 5 inches in depth. Consider a pine wood for cheaper boxes, or an oak wood for more grandiose boxes.
If you want something more dramatic, then you should choose a darker wood, such as maple or mahogany. Look for dark woods which have character, but which are also strong enough to hold up your object. Dark woods can sometimes overwhelm the items in a shadowbox, so restrict your use of these to very simple lines.