The most important thing is the Psycho shower curtain. I've been using this shower curtain for about thirteen years, simply because I haven't been able to find another. It has undergone numerous repairs and the holes have been fixed several times. I've seen other curtains in this same vein, but no others were licensed by Universal and usually look cheesy. This is the only one I've found that says Psycho and has the trademarked image of Mother holding the knife.
Next is the skull and wig that I keep on the back of the toilet. I thought about keeping a bloody knife next to it, but I elected against it for safety reasons.
On the wall I have a lithograph of Janet Leigh screaming her face off.
The only colors in the bathroom are red, black and white. The floor is black and white checked which looks great against the red floor mat and towels. I find this a nice alternative to other parts where I live which have been Empire Strikes Back themed for about thirty years.