Lauren I love the look of barn doors.

Real Sliding Hardware Real Sliding Hardware sells barn door kits as well as sliding barn door hardware! Take a look:
http://www.realslidinghardware.com/barn-door-hardware/

Basin Custom We have barn door tracks. We can customize size and color! http://www.basincustom.com

Rustica Hardware We have just added many hanging systems (some very unique) to our line of hardware. See: http://rusticahardware.com/hardware/

motherbear Knotty pine, if I had to guess.

DecoDesignCenter.com Count me in for knotty alder wood as well.

Real Sliding Hardware Real Carriage Door Company makes custom sliding doors and hardware. You can see their work at: http://www.realcarriagedoors.com/gallery-sliding-barn-doors.php

Heather Swallow This picture on another site: said this door is a reclaimed one-of-a-kind find from off an old barn or other outbuilding, as I recall. Probably cost the original owner less than $1.25 to build it themselves. Check out the reclaimed wood sources in your area, or Craig's List or similar sometimes has reclaimed barn wood for sale. I dealt with Real Carriage Door and can vouch for their excellent quality hardware. Didn't buy a door from 'em. Made it myself from cedar planks just like ol' grandad did. Well, he used pine or fir probably, but I like cedar for a laundry room. Keeps out the moths.