Well, French beans are my favourite crop, but everyone else has voted for them.

I'll go for Rainbow Chard - use as spinach, but easier to grow. I've had leaves available for picking for 9 months of the year. They are a beautiful plant with yellow, pink, white or red stems.
They make superb guinea pig/chicken/rabbit fodder too.

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~ What do I think of Western civilisation? I think it would be a very good idea ~ Gandhi