Boltonia (doll's daisy): This North American native looks a lot like an aster, with white or pink flowers, only on steroids. It can grow, shrublike, to 6 feet. Grow in full sun. It's hardy in Zones 4-9.
Canna: Big leaves and boldly colored flowers (red, orange, yellow or pink) add drama to a garden. They generally range from 5 to 8 feet tall, but the tallest, C. 'Musafolia,' can get to 12 feet in a warm, moist spot. These are tropical plants, so gardeners here will have to dig and store the rhizomes in a cool, dry place, or simply treat them like annuals. Grow in full sun.
Cleome: Also known as spider flowers, these full-sun lovers grow up to 6 feet tall and have distinctive pink, white or purple flowers. They're easy to grow from seed and attract hummingbird moths. They're grown as annuals outside of tropical zones.
Cosmos: This delicate-looking flower with its fernlike leaves is tough as nails and easy to grow from seed. Their lacy look makes them great filler plants, too. Cosmos need full sun, but will thrive in ordinary soil. Butterflies and bees love them. Sensation is just one of the taller varieties, topping out at 4 feet. The annuals bloom summer through fall.
Delphinium: A summer garden staple, the majestic perennials grow to 6 feet and have beautiful blooms that attract butterflies. They often need staking, can be fussy and prefer rich soil to produce good-size blooms. Full sun to partial shade. Several varieties are hardy in zone 4.
Hollyhock: Tall, colorful and old-fashioned, they need sun and moisture and will grow to 6 feet or more. Many varieties are biennial and die off after two years, but they often self-seed.
Joe-Pye weed: Another native perennial, this butterfly magnet does well (7 feet) in moist soil and has a flat top clustered with flowers. It likes full sun but can tolerate some light shade. Blooms in July and August.
Sunflower: If you want them really tall, buy one of the older varieties and plant them in full sun. What's more impressive than a 10- or 15-foot-tall plant with a basketball-size flower on top? Some of the taller varieties: American Giant Hybrid, Mammoth and Skyscraper.
Zinnia: These popular annuals have been downsized in a search for compact, more disease-resistant varieties. But the 4-footers still have a lot to offer: They're easy to grow from seed, are colorful and keep producing till frost. Taller varieties include State Fair, California Giant, My Lucky Ladies and Big Red. They like well-drained soil and become drought-tolerant once their roots are established.