I have two. A 1686 penny from Jamestown, VA in 'decent' condition (Decent enough that the my local coin shop could identify it after a couple hours of examining it xD) And a 2004 Schwinn Sting-Ray Chopper Bike endorsed by OCC Choppers. Originally sold for $400, there was only 2500 produced of the variant I have, and the one I own still has the stickers in the spokes and the frame, and is in perfect, untouched condition.
I guess the rarest thing I own is either my copy of The House of 1000 Corpses script, signed personally to me by Bill Moseley who played Otis (it's signed "John, go f*** yourself. Love, Bill Moseley") or my Opeth VIP pass; they had a tour for their 20th anniversary, only 6 concerts across the globe and VIP tickets were damn expensive, got a bunch of stuff signed backstage too. Edit: the script text isn't censored obviously, that's just TA.
Autographed Babe Ruth Button, and Michael Phelps, and Travis Pastrana (bestfriend used to live next door to him! ) and uhm.....a piece of Pearl Harbour and the Berlin Wall
Sad thing is that I actually thought of that when I read the thread title. Hmm... I don't know. I have some old coins from the late 1890's or something. Haha I have no idea. A fully working super nintendo with all the classics on it?
Come to think of it I own a bunch of items that are one of a kind, but they're not especially interesting or valuable. I've got a custom-made plush toy... it's a boy in a yellow wolf costume.
The United States Declaration of Independence [1776]. I've stored it in the National Archives, Washington (DC), for security reasons.
Holy fetch! I've never seen one on those before! How long have you had it!?! Haha jk, 8 of my friends have 360's and only 6 of them have gotten the red ring. However, myself and my 4 other friends with PS3's haven't had any problems. Umm... So I found my little locked container where I keep all of my "rare" stuff that's actually valuable, but I can't find the key. Effffff.....
