I grew these last summer from seed. (Zinnias are one flower that grow best from seed-meaning, just plant the seeds directly in the ground. They like full sun and don't like wet feet-meaning, they will rot if they are not in well-drained soil.)
It's amazing to me that you can buy a few 10 cent or 25 cent seed packets from the dollar store and end up with beautiful flowers like these.
Sunflowers, nasturtiums (they do best in bad soil and you can eat the flowers), bachelor buttons, cosmos, and morning glories are all easily grown from seed.
Those pictures are almost making me long for summer. Almost.