What would be a good soil mix for a raised bed?

FAQ
Question: 

What would be a good soil mix for a raised bed?

Answer: 

An excellent soil mix can be prepared by mixing equal parts topsoil, organic matter (compost, well-rotted manure, or peat), and coarse sand. 

Before filling a raised bed, work up the existing soil with a rototiller or spade.  Add a few inches of the soil mix, then incorporate it into the existing soil.  Continue to add and incorporate additional soil mix until the raised bed is filled.  Incorporating the soil mix into the existing soil prevents the formation of distinct layers in the raised bed.  Distinct layers of soil may impede water movement and discourage root growth.