Cowpeas also known as Black Eyed Peas are a great source of protein and grow like mad in my heirloom garden. 2 packs of seed made about a 30 foot row and produced nearly 4 pounds of shelled "peas." Blackeyed peas are actually a bean. Read more at Friends Drift Inn blog.
A cold frame with a glass top can give you a 12-month growing season, even in Maine, and it's the easiest and most economical way to extend your harvest. Build the one described here, and you're on your way to fresh veggies year round.