MTBs are popular for touring, but you need the right kind, that wont break down miles from a bike shop.
Get a steel frame, no suspension fork, and plenty of braze-ons.
Soma do a good tourable old-school MTB frame.
http://www.somafab.com/groove.html
http://www.waterfordbikes.com/gunnar/data/mainframe.htm
or 26" tourer:
http://www.bgcycles.com/blt.html see the BLT-x
For a touring build spec, pay close attention to the BTL