The Tumblr called Capitol Couture is fantastic. It is written as if the books are real and it focuses on the story line, as well as the fashion we'll see in the film. Read the site's masthead:
Whether you're a Capitol fashionista seeking inspiration for your latest look or a District citizen tracking rumors about the Tributes and other celebs, Capitol Couture is the only place to turn for pictures and news reports on the fashion, trends and lifestyle that make Capitol living so grand.
Sorry, the site takes forever to load, but it's still pretty great.
Also, EW has an exclusive photo of the costumes for the tribute parade. I can't wait to see them on fire.