First off, the first of my larkspur blooms this year. These come in all different shades of blue and pink and red. They are easy and often will come back the next year on their own. One thing I really like about them is how the hummingbirds love them. Their are different types, but the ones I have get pretty tall - 4'. They melt in the Louisiana heat around May. Plant them in October down here.
Next up, some Telstar Picotee Dianthus. These little rascals are prolific! They stay covered in blossoms and should bloom till around May. The Telstar variety is a Louisiana Select one and should do well all over the South. I think this would also be a perfect candidate for container planting. It gets about a foot tall.
Last, is a close-up of one of my Old Spice sweetpea flowers. Old Spice is supposed to take the heat better than other types. It still melts away around April down here. Right now I have a section of fence covered with these vines and the fragrance really wafts on a still day. Mine are all different colors from this wine red to lavender blue. If you deadhead the flowers when they fade, the vines will keep producing blooms longer. Plant them in late October / early November in the deep South. This is about the only cool season annual vine I know of for down here, but it's a good one.