My neighbors tore out their old cement porch last summer to install a wood deck. I eyed the stacks of discarded cinder blocks on their curb for an entire weekend, wondering what I could use them for. If I'd seen this idea back then, I would have grabbed them and put them to use.
This beautiful, functional idea comes via Annette at Potted. She built a low wall from cinder blocks, attaching them to each other with a weather-safe adhesive. The blocks are lined with wire hardware cloth, then a layer of broken block covers the hardware cloth to keep the soil in each section. She has planted the wall with succulents, which makes since because this would probably dry out fairly quickly. I can also see it planted up with Mediterranean herbs, such as rosemary, thyme, and oregano, which prefer things a bit on the dry side.
You could also make a small version of this, maybe around the edges of a porch or deck. Some people build their raised garden beds with cinder blocks -- instead of covering the holes, why not plant them up with some small vegetables or herbs? Next time you see someone tossing out cinder blocks, keep this idea in mind!