Going back to the subject of gabions, I must say that I looked very seriously at using them to build my retaining walls. I really like them, they're cheap, easy to use and can be very eco-friendly if they're filled with old rubble. Also you can plant into them and the crevices make great hiding places for insects and other wildlife. I can imagine that filled with herbs they'd make a wonderful feature.
Anything to do with environmental building projects.