He wrote a scifi short story called "Firstborn", which I think can be read on Tor's website, and a fantasy short story about with Roaden, Sarene, and Ashe that I think was called "The Hope of Elantris." I haven't read Firstborn, but the Elantris one is pretty good, and also really short, if I remember correctly.
He has "The Emperor's Soul", a novella that's about to be released in November (though some bookstores already have copies on the shelf). "Dragonsteel", the book Brandon wrote for his college thesis, is also floating around somewhere at BYU I think, but it's really hard to get your hand on that because it's not actually published. Also, in the Mistborn Adventure Game book there's a short story about Kelsier called "The Eleventh Metal", which I haven't read but reeeeally want to.
You can also find a few chapters of his abandoned novel "The Liar of Partinel" online, which tells about Hoid.
EDIT: I also forgot to mention the Alcatraz books, which is a YA series. I haven't read it, but from what I can gather it leans toward a more fun, comical tone as opposed to the serious ones in his adult novels. He's also finishing Wheel of Time, but I guess that doesn't really count as part of his original works.
So, to consolidate it, here's some more to add:
Firstborn
The Hope of Elantris
The Emperor's Soul (official release in November but is already sort of out
Dragonsteel
The Liar of Partinel
The Eleventh Metal
EDIT: Alcatraz Series
Hope that helps! And if you're just looking for something by Sanderson to read until his next book comes out, I'd recommend checking out his website. You can read deleted scenes taken from early drafts of his books, and I found them pretty entertaining to read.