What plants will attract beneficial insects to my allotment garden?

I'm planting Marigolds and Nasturtiums and have heard that the Poaced Egg plant is good for attracting hoverflies. Anything else I should be thinking of?
Update: oops - that should have been Poached Egg plant. I'm growing vegetables - tomatoes, corn, courgettes, herbs, onions, the usual stuff - in an allotment in North London.
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