Here is a list of the flatwater outfitters I am familiar with; if you know of others please let me know and I will add them to the list:
On the Flint river near Huntsville: http://www.nacktrips.com/
On Big Wills creek near Gadsden: http://bigwillsoutfitters.com/
On Terrapin creek near Piedmont: http://www.canoeshop.net/
Just over the border in Tennessee on Elk creek: http://www.kelsocanoe.com/