Some plants, like humans, do well in the heat of summer. Others suffer from fungus problems and wilting on hot days. Planting annuals and perennials that do well is an asset to your landscape and great for the summer gardener. Also, these plants work well in bad soil.
The first annuals that come to mind are those sold at the large stores and supermarkets, such as petunias and marigold, or begonias. All these do indeed do well with minimum care throughout the summer. Others though should also be considered.
Sunflowers are always fun if you have children, Pick the ones that grow to eight feet or so tall and watch them grow, seemingly at an inch a minute. Sunflowers come in all manner of different shades of oranges and yellow, as well as a range in heights, so pick one to suit your garden style.
Look for Mexican sunflowers too (Tithonia rotundifolia) which are smaller than traditional sunflowers but bloom all through a hot and steamy summer.
Salvias also do well in the summer. The common annual red salvia is just one of the many different varieties that come in white, blue, pink and range in height from about one foot to nearly three feet. Pineapple sage (Salvia elegans) can also be used in teas as well as giving the hummingbirds a good send-off in September.
Unfortunately, this plant has a tendency to flower late and in zone five and above, may not produce flowers before the first frost hits. If the frost is light though, it is well worth the effort to cover this plant and see its bright red flowers.
Verbena bonariencis, and Heliotrope (Heliotrope arborescence) both have purple flowers from early summer through to the fall. and fit into most gardens .
Annual vines that come from the south make a colorful addition to any fences that you have. Black Eyed Susan vine ( Thunbergia alata), as well as Sweet Potato Vines, Blackie and Marguerite (Ipomoea batatas) and Moonflowers (Ipomoea alba) and Hyacinth Bean (Lablab purpureus) should all be great for color in the summer for you, although they will need to be started indoors in the northern tier, so that they get established enough to flower by the end of July or so.
Take care with the seeds of both the Ipomoea and Lablab, as they are dangerous to ingest.