I have found a few websites that are useful. So, enjoy the links for as long as they are available.
Wikipedia has a nice article for the earlier part of the century. http://en.wikipedia.org/wiki/1795-1820_in_fashion
Regency period extended into the first part of the century. In fact for 37 years of it. Here's a link with some neat resources. http://www.regencyreproductions.com/
Victorian Era Fashion, excellent site. But limited to Victorian era. http://www.fashion-era.com/the_victorian_era.htm
Limited site but useful information http://gallery.sjsu.edu/paris/fashion/ 19th century Paris women's fashions
Ladies Fashion was highly affected by the periodicals of the time period as well. Godey's Lady's Book was quite popular, not just for the color plates of ladies fashions but also for their fictional stories.
Another thing to keep in mind, is what were the fashions of the area you're writing about. For example, in the mid century in Key West, FL. There was a mixture of NY fashion, Southern and Spanish. Corsets didn't last long there, or at least the women didn't wear them too often during the heat of the day. Different cultures brought different fashion attire.