A photoshopped image of Obi Wan-Kenobi’s body with my dad’s head. His students did it in lab one day, and he sent me a copy.
Weaponry, including but not limited to: A 70 year-old recurved bow, some arrows, a double-headed axe, a sword and a very nice flail.
To offset the somewhat scary atmosphere, my wife wants me to hang up her Tibeten prayer wheel.
An original print of a rainbow serpent dreaming story painted by an Aboriginal Australian.
A little note from a fortune cookie taped to the wall saying “You will conquer all obstacles and achieve success.”
A company calendar, open to November: National Diabetes Month!
It’s a tie:
(No, I don’t mean there’s a tie on the wall.)
a fairly disturbing self-portrait
a huge map of the U.S., including Alaska and Hawaii!
On the back wall of my cubicle at work I have an expired VFR Terminal Area Chart of the Baltimore-Washington airspace. On the shelf above my desk I have an origami crane and waterbomb, the latter made from a sheet of D-sized paper. It’s about 8" in each dimension.
At home I have a few of those photomosaic posters, but I want to cover one wall with a continuous set of aeronautical charts.
-Aviation Geek 
The most interesting contrast has to be on the shelf with all the family portraits on it. There are pictures of me and my siblings and a vase and a couple of oil lamps. Over everything there’s a big flowery wreath that one of my mother’s friends made her. Right in the middle of the shelf my father has placed a model of the Exide NASCAR from '99. The more you look at it, the weirder it seems.
A fly.
(I’ve removed his vocal chords.)
In which chords was he vocalizing?
Poor fly. 
Like Kal, Some weaponry:
A model 1886 Winchester rifle in poor shape
An MBA Mark-1 model B Gyrojet rocket pistol with an engineering schematic breakdown of the gun, and two rockets, one of which is one of the original prototypes from when the gun was tested.
Both are in shadowboxes…
I had no idea when I posted the OP that the answers would be so diverse and fascinating!
You know…those stiff upright thingies that enclose a room.
The most interesting thing in my room is probably a letter from Katharine Hepburn.
The weirdest is a wooden pub sign, a reproducation, that says SILENT WOMAN and has a rendering of a decapitated woman in mid-1700’s dress.
The Sherlock Holmes type Inverness coat and cape is kinda fun too.
For those of you who have blank walls — why?
An Aboriginal Australian war club, painted and incised, with a spike in one end. Also a self portrait, but that’s not so interesting to me.
A WWI German bayonet/sword thingy.
Oh! and hanging from the hook that holds the sword, is a set of keys that I have no idea what they go to, and the keys are on a ZZ Top keychain. They’ve been there since the late '80’s.
I have the group photograph of the graduating class of the university of Michigan Medical school Class of 1930.
My home computer is in the dining room, so it’s all fairly conventional. My favorite is a desert scene that my mom painted. Also a postcard of a drawing of a woman screaming tucked in above the thermostat.
A picture of the 1969 Mets outfield, autographed by all three men, Tommy Agee, Cleon Jones, and Ron Swoboda.
2500 orange icicle lights and a cardboard Dracula.
Miles Davis and his trumpet
2001 movie poster
Dali print of “The Meditative Rose”
Framed copy of the original Metropolis movie poster
Photomosaic of Darth Vader
A calendar and nothing else.