Parsley, (Petroselinum crispum L) can take some competition and fends for itself in a maze of wild flowers in my garden.  It is a frequent addition to potato dishes, and a pinch on pasta, macaroni salad, hummus is always welcome.  (More) 
Italian parsley, often preferred over P. crispum.  May be brought inside in winter and will continue to grow.

Eating parsley may help prevent calcium oxalate stones (Commission E).