Day Lillies! I think they are called "Stella De Ora", in plant terms. They are so strong and really tolerant of weather and growers who are learning. Just plant and water and watch them thrive. They are a prennial so you just trim them back through the winter and they bounce right back in the spring. They come in yellows and reds and are really affordable. They will spread through, especially if you keep them for several years.
You could start with growing Black-eyed Susans, Day lily, Marigolds and Cosmos. All are flowers that will not die if you forget a water or two. Will be fine in just about any soil condition and they do not need alot of attention. I hope this helps you out.
I have made a hub about this. I am an expert for this. Just for example, you can plant many flowers but before that read some of the Easy Tips in Taking Care of Flower Garden Plants, just in my hubs here.
"So when you buy a flowering plants for your flower garden, try to choose properly the type of flowers that suit the environment of your area either four season country, tropical countries, etc."