We are heading into the time of the year that folks start thinking it's to late to start seed, when in fact there is almost always seeds to be started. When we embrace annual seed starting fully--- both cool and warm season, the possibilities are endless. Part of the secret sauce to a longer and easier season is to learn when to plant each group in your garden and to run with it! 
Checkout:
Warm-season flower seeds.
Cool-season flower seeds. 
Seed-starting equipment.