There are hundreds of single-petaled and double-petaled varieties attainable. The common ones are sold in most garden centers while the rare, exotic hybrids can be purchased at specialty nurseries and plant shows.
Hibiscus plants come in all the different colors, from most common reds to pinks, yellows, lavenders and blues to whites, browns and golds.
The tallest kinds can grow as tall as 10 to 15 feet and others are only a few feet tall. Since these plants are so easy to shape by pruning in early spring, in Florida hibiscus is frequently used as a hedge, especially around the business buildings.
For all the frugal gardeners out there and especially the ones who enjoy growing everything from seeds, here's some good news: growing hibiscus from seed is very easy!
Lots of amazing photos of hibiscus' blooms and useful information can be found at http://www.internationalhibiscussociety.org/