I have a confession to make: I have never had formal, raised beds in my garden, just piling up the soil to create a mound into which I would plant. But now, I have joined the Community of Gardeners who "work smarter, not harder" and am building raised beds. Raised beds with sides have a lot of advantages: they drain better, warm up faster in spring and have fewer weeds. You can make a good soil mix, adding compost each season, and it won't wash away in heavy downpour.
Here are three of the four my husband and I built (guided by my Dad). They are not yet in their final spots, nor are they filled (which I intend to do with garden compost, and a mix of topsoil and mushroom compost). Due to a vole problem, I am lining the bottoms of the frames with fine mesh hardware cloth/fencing, to deter the pests (we will flip the beds after I affix the cloth on each).
For some instructions in building raised beds, go to:
http://www.organicgardening.com/learn-and-grow/how-to-build-a-raised-bed
Happy Gardening!