Here's a list of companion plants, that may benefit the plants in your garden when planted in close proximity to each other.
My favorites are geraniums and marigolds.
Aster - repels most insects
Basil - repels flies and mosquitoes
Borage - tomato worms.
Caraway - loosens the soil and attracts parasitic wasps and bees.
Coriander - repels aphids.
Fennel - potato bugs.
Geraniums - attracts caterpillars, luring them away from nearby plants.
Horseradish - deters potato bugs.
Larkspur, protects vines against vine beetles.
Lavender - attracts pollinating insects.
Marigolds - discourages most pests.
Mint - deters white cabbage moth.
Oregano - repels aphids.
onions, garlic, chives & shallots - these repel. slugs, aphids, cabbage worms
Parsley, repels carrot flies.
Plants to attract beneficial insects.
Although nectar is collected from any flower, my favourites are the nettle-leaved bellflower, Campanula latifolia, in soft grey-lilac, and Brantwood in deep blue. These are loved by bees.
Here is a great link from the RHS perfect pollinator list