the room: diffusors, absorbers, plants, books, mdf

I'm just putting my first system into place. I was having brightness problems which lead to rapid listening fatigue. My room is 8' tall, 13' wide and 19' long, thick plaster walls, hardwood floor (large throw rug) and lots of big windows. I've treated the room with covering windows with heavy cotton sheets (drapes are on the way), hanging throw rugs on the corners of the front wall and back wall, bookshelves on the back wall. The sound is much better, however ... it really looks terrible. I'm thinking of placing fiber board covered with fabric (12'' by 8') in the corners, first reflexion and behind the speakers. Also to place book shelves and large plants on the front and side walls. Help before I've started!? What's the best, least expensive way to tweak my room so that it still looks good.

Thanks
andrew