Petunias are an old favorite flower of gardeners. A relative of tobacco, they come in two major types, grandiflora and multiflora. Grandiflora petunias are larger than multifloras, so they don't stand up as well to the elements. Multiflora petunias are the ones used commonly in garden borders and containers. These plants love sun and are drought tolerant, which is perfect considering that you likely will not have any shade sources around your pole. The red varieties are easy to find in garden stores, but other colors are available. Blue varieties tend to be a bit more purplish than blue but still work.
Alyssum is a small ground cover and border plant that usually stays around 6 inches tall. The flowers on this plant are tiny, but they are prolific, appearing over the majority of the plant. Alyssum comes in a rainbow of colors, but probably the most common and widely recognized is the white variety. This variety is known as "Carpet of Snow." Alyssum tolerates sun but it needs well-drained soil and plenty of water.
Dianthus is a mid-sized flower that tops out around a foot and a half high. It can spread one to three feet, however. The flowers on this plant are dual-toned, with the darker pigment in the center. The petals have ragged edges. The red and white variety works well for poles with American flags, since it has not one but two tones of the flag. Like petunias, dianthus plants like full sun.
Balloon flowers have large, blue blooms that look like a star in shape. It can tolerate some shade but prefers full sun. This plant is a better choice if you have a taller pole, as the plants can get up to 3 feet in height.
Every state and nation has different colors on its flag, so you may have to use other varieties around your pole to accommodate this. In general, your state or national flower usually is a good choice, unless it does not do well in full sun. The national flower for the United States is the rose -- you can plant full sized plants around the pole or put some miniature varieties in containers. Marigolds also are patriotic -- the government has received proposals to replace the rose due to their hardiness and the fact they grow well in every state of the union. Don't forget about flowering shrubs like rhododendrons or azaleas.