This picture frame collage is neat. I love the font on the wall and I adore the famed initial in the middle. This would take up a good chunk of our huge living room wall so my wall won't look so naked.
DIY wainscoting with strips of wood. -- Use Rust-Oleum to paint outdated brass faucets and fixtures! -- 27 Easy Remodeling Projects That Will Completely Transform Your Home - but in a dark brown or a color to match the living room furniture
Hidden doors -- This company makes cabinets, bookshelves and anything you can think of that fits your existing doorjambs thus hiding the door (and also making use of the space) Not sure I like the idea of a 'gun cabinet' door.