Just finished up the first invite for this year. Seeing it's Ghost Town theme, I went with TNT invites, as it'll be part of the decor (TNT, Wells Fargo bags, etc).
The TNT is made of 1 1/2" pvc. I closed up one end, rolled up the invite inside, and closed the other end. The invitee opens the tube by pulling on the red and yellow flame-tipped wick. Inside is a personalized "Wanted" poster.