I'm a big fan of the shape of a keyhole garden. It's a shape that really helps exploit a lot of permaculture principles. I had a mandala shaped bed, which was actually 5 or 6 different keyhole beds all touching each other. It was really neat and very productive for us. I took it apart and used all the material to build a butterfly garden for Trish.
The height question
@Seedfork mentioned is also something that has always puzzled me. My herb spiral is really tall and filled with mostly wood and good soil and compost in just the top 12 inches or so. Most of the keyhole beds I've seen are lower to the ground, like any other traditional raised bed. But occasionally someone puts together a bed that's 3 or 4 feet tall and I don't really know why they do it except to make it more accessible to people.
Check out my hugelkultur article for photos of my mandala bed:
http://garden.org/ideas/view/d...
