One "source" tell me that horseradish increases the disease resistance of
potatoes, and that alliums (onions) also help all of the nightshades (
potatoes, tomatoes,
peppers). BUT don't plant tomatoes &
potatoes too close. Another does say that beans, corn, cabbage all are compatible. But again, no tomatoes, and no sunflowers. Also-- French marigolds are good for
potatoes.
Remember to consider timing & space when you're thinking about planting "between the rows." Bush beans will be ready to pick roughly 55 days from planting, be sure to leave yourself some space to get to them (the voice of experience talking here!).
Hope this is helpful. Good luck!