Grow borage for its incredibly pretty edible flowers. It's very easy to cultivate, and produces clusters of delicate flowers of an intense moroccan blue. Add them as decoration to salads, or even better, freeze them individually in ice cubes for a stunning twist to G&Ts, pimms etc.
When you've grown it once, it will self seed and you'll find plants popping up in your garden for years to come.
Equally suited to plots or patios.