Calendula, which I actually consider more of an herb than a flower, is a sunny, yellow or orange, daisy-like flower. It makes a great companion plant for almost all crops in your garden.
Nasturtium is a vining flower that has a strong scent and peppery flavored leaves. It can be a great trap crop for aphids. And it has repellent qualities for other pests including squash bugs, potato beetles, and other beetles.
Sunflowers are a wonderful addition to any vegetable garden. They attract tons of pollinators. You can use them as a living trellis to grow pole beans or other climbing crops up.
I plant it near eggplant and peppers to help with flea beetles and around brassicas to help with the cabbage butterfly.