For the last few years, we've been using a combination of vetch and fall rye for a cover crop (above). Cover crops have the benefit of keeping the weeds down, of providing protection for our young vegetable seedlings until they're established in the spring, and above all of enhancing the soil when our garden beds are fallow (vetch puts nitrogen in the soil, and rye is a great mulch when you mow it down in the spring).
Lately, though, we've actually begun EATING a little of the cover crop, too! Here's the deal: we've recently bought one of those super-duper blenders, with a motor big enough to power the space shuttle, and as a result have been having these amazing smoothies every morning: some kind of green (kale, chard, parsley, young nettles, dandelion leaves, chickweed, left-over lettuce) and some fruit (bananas, pineapple, blueberries or raspberries). The main issue is to vary the kind of green you're using from day to day, and for my money, to make it taste as good as possible in the bargain.
We've recently added a bit of the vetch-rye cover crop to our smoothies, too: we've been using our winter kale, leaves from some cabbage that bolted in the cold weather, dandelions from around the yard - so why not a bit of crop cover, too? These green smoothies are a great spring tonic - they really bump up your energy and raise your spirits as we wait for spring weather to arrive!