This is not as simple as it seems to be. You want flowers that will stand up to hot climates, ones that will attract bees to pollinate your vegetable or if you are just looking for the simple beauty of them you must know that your choices are almost completely limitless.
So now consider these options based on the different categories you have available to you.
Heat Tolerant Flowers
The Blanket Flower are known for being able to withstand drought and tolerate heat pretty well. It is a perennial that provides color all summer long. The downside of these flowers is that they are short-lived, although they bloom easily.
The Veronica is a beautiful purple spike flower that grows well in the summer. If you live in the south it will need to be planted in the shade, but in the north it thrives in the sun.
Beautiful and Vibrant Colors
The Tall Garden Phlox is a four-foot flower that grows bunches of pink flowers together. They are sweet-smelling and beautiful to look at.
Asters are found in a myriad of colors. From white to rich blues and purples, these flowers will soon be a staple in your summer and fall garden. They grow great in combination with other flowers.
Flowers to Attract Bees
Early bloomers attract bees and butterflies. This is essential to growing many fruits and vegetables. You can have beautiful flowers that will add beauty will providing you with the needs pollinators.
The Hawthorn is a very fragrant flower. The bloom in May and will attract most nectar-feeding insects. You can plant them in front of your vegetables, like squash or zucchini, so that you have the bees right where you need them to be.
Forget- me-not is a tiny little blue flower. They bloom all spring long and will bring in the crucial insects through most of the summer. 
Rosemary makes a small white flower in summer when most the attracting flowers are starting to die off. These will make your whole garden fragrant. You can plant them in a pot near your garden so that you can pluck them for cooking.
No matter the flower that you do pick, the enjoyment of watching your garden grow is magnificent. It is a relaxing pastime that gives you the benefits of fresh air and sunshine. That is the greatest reward. So go and have some fun choosing which flowers are best for your garden.