Try Auralex (think it's auralex.com), or do a search. They have a service which will suggest treatment(s) depending upon you actual room configuration and sonic complaint.
If there is a Guitar Center store in your area, they will have a catalog and perhaps some treatments on display.
If you can get Owens Corning 703 fiber boards they work as well and in many cases better than many of the products mentioned. Take the fiber board and cover it in a loosely woven cloth and hange it where needed (generally at the first reflection points and sometimes behind the speakers depending on their type). This also looks considerably better than the Sonex or RPG solutions.