BEANS:
All bean enrich the soil with nitrogen fixed from the air. In general, they are good company for carrots, brassicas, beets, and cucumbers. Ideal for heavy nitrogen users like corn and grain plants. French Haricot beans, sweet corn and melons are a good combo. Keep beans away from the alliums.

CHIVES:
Improves growth and flavour of carrots and tomatoes. Chives may drive away Japanese beetles and carrot rust fly. Planted among apple trees it may help prevent scab. A tea of chives may be used on cucumbers to avoid downy mildew.

NASTURTIUMS:
Plant as a barrier around tomatoes, radishes, cabbage,  cucumbers, and under fruit trees. Deters woolly aphids, whiteflies,  squash bug, cucumber beetles and other pests of the cucurbit family.  Great trap crop for aphids (in particular the black aphids) which it does attract, especially the yellow flowering varieties. Likes poor soil with little moisture and no fertiliser. It has been the practice of some fruit growers that planting nasturtiums every year in the root zone of fruit trees allow the trees to take up the pungent odour of the plants and repel bugs. It has no taste effect on the fruit. A  nice variety to grow is Alaska which has beautiful green and white variegated leaves. The leaves, flowers and seeds are all edible and wonderful in salads!

PARSLEY:
Plant among and sprinkle on tomatoes, and asparagus. Use as a tea to ward off asparagus beetles. Attracts hoverflies. Let some go to seed to attract the tiny parasitic wasps. Parsley increases the fragrance of roses when planted around their base.


Source:
http://www.pssurvival.com