Red is a "warm" color. Red flowers can be used to influence one's perception of a landscape. For instance, using them in a border can draw attention to that particular area of your yard -- and away from another. So if you'd just as soon not have viewer's gazing at point A in your landscape, take matters into your own hands and plant blooms of this color at point B.
View my pictures of red flowers to help with plant selection. In addition to pictures of red flowers, I also provide examples of foliage and seed pods that bear this vibrant color.