As has already been stated, too much absorption can result in a room sounding dead, lifeless. For those rooms diffusion is a good alternative. GIK's wood 1D diffusers are currently out-of-production, but are available from ATS Acoustics and others.
GIK offers 1D diffusers made of EPS, the Gridfuser (a carton of four 2' x 2' panels for $214, white only, though paintable). Vicoustic offers both 1D and 2D in EPS, the Trap Fuser (a carton of six 2' x 2' panels for $499) and the Mulifuser DC2 (a carton of six for $699), both in white, grey, and black.