Hidden doors -- This company makes doors, bookshelves and anything you can think of that fits your existing doorjambs thus hiding the door (and also making use of the space). If you click through checkout the "gun cabinet" door. Lots of great ideas.
Harry Potter posters // I love how beautifully perfect they represent each one. Especially the last one, how they have Nagini's head separated from the body, it represents the last horcrux being separated from Tom Riddle. It shows his death. Wow.