There are only a couple of companies that come to mind that offer the whole gamut of acoustic treatment products: diffusers, panels, bass traps, etc. If you need everything, or would like to mix and match products, I would recommend using an acoustician to specify product and placement.
Each vendor may be able to offer some general guidelines, but being unfamiliar with all products to be used, the whole picture may not be clear. You'll want a good balance of treatment. You won't want your room to be too dead. If you buy treatment for early reflections from one guy and buy broadband bass traps from another, you may end up with too much HF damping in the room when combined.
An acoustician will be able to calculate exactly how much material is needed to treat different areas of the audio spectrum in order to get the decay time right for your room. It's not as simple as saying, "put a couple of panels here and there." What are the dimensions of your room? What materials were used to build the walls? Sheet-rock. OK, how thick is the sheet-rock? Single layer, double layer? Is there a cement wall behind the sheet-rock or an adjoining room? Carpet, tile, or wood floor? All of these things and more need to be considered in order for the acoustician to specify how much early reflection treatment, broadband bass treatment, tuned bass treatment and diffusion is necessary to get your decay time along the entire audio spectrum under control. In smaller rooms bass trapping is going to be particularly important. Speaker placement in relation to the walls and listening position is also something that a good acoustician will be able to specify.