Historical Southern Fashion
From the Wikipedia article on seersucker:
Seersucker was first used in the United States by the working class but was later adopted by the upper classes. The material was considered a mainstay of the summer wardrobe of Southern gentlemen, who favored the light fabric in the high heat and humidity of the American South.
Seersucker is still widely worn in the South between Easter weekend and Labor Day, where it is often accompanied by a bow tie. It is widely considered a fashion faux pas to wear seersucker at the wrong time of the year, although in warmer climates this rule is often ignored.
(A Wikipedia update: Seersucker is still widely worn in the South between Easter weekend and Labor Day, where it is often accompanied by a bow tie. Easter can come too early to wear seersucker since Confederate Memorial Day (The 4th Monday in April) is considered the actual appropriate time for this style of dress. It is widely considered a fashion faux pas to wear seersucker at the wrong time of the year.
Article on a Mississippi senator's re-introduction of seersucker. Washington is part of the South, and seersucker was common until the widespread use of air conditioning.
An article from the U.S. Senate website on Seersucker Thursday.
17 June 2009 update: I just received the 8 June issue of New York magazine, which features an article about and photo (by Tabitha Soren!) of Michael Lewis in a blue-and-white seersucker suit, yellow tie, white bucks, and white socks. Naturally, he's from New Orleans, one of a few Southern preppy men who've gone North and found success in the media elite. Jon Meacham is another, and also C. Shelby Coffee III, former editor of The Los Angeles Times.
31 December 2009 update: I found this by chance a few days ago: http://www.gastrochic.com/2009/fashion/wasps-what-they-really-wear/
Note: "Southern preps in particular love bright colors, whereas their northern counterparts tend to stick to navy."
Southern Designers and Labels
Ruff Hewn (co-founded in 1981 by Ernest Lee Marchman with his son Dennis)
The South is Sexy
Books and Films Which Address Southern Style, In Whole or In Part
Queen of the Turtle Derby and Other Southern Phenomena, by Julia Reed
A review from the 9 May 2004 issue of The New York Times.