If you don't mind some extra work, what people often do who are looking for big, showy flowers is dahlias, especially the large variety known as dinner plate dahlias. Their flower blossoms do get to be 12" across and again in whole range of brilliant colors and stripes:
https://bloomiq.com/sites/bloomiq.com/fi ... 72.002.jpg
They are perennials, but tender perennials. They are generally only cold hardy in zone 8, places like California and TX.
The rest of us, if we want dahlias, dig them up in the fall and store the roots, wrapped in newspaper in a cardboard box, somewhere that stays between 40 - 50 deg and does not freeze.
If you are willing to dig and store your dahlias, you can have the biggest, showiest flowers in the neighborhood!