With stuff like racks and bags and whatnot, a range of prices is probably the most important. I really like Topeak, but it doesn't seem to be big in the US. But you'd probably also want something high-end like Tubus or Old Man Mountain.
Panniers...well, you'll be laughed at if you don't stock Ortlieb. But again, you need cheaper stuff like Topeak, Deuter, Axiom...
Also, an extensive mail-order catalogue - people get particular, and it helps if you can order the exact bit they need.
Have you considered being one of the first shops to stock EpicDesigns/CarouselDesignWorks gear? Get in touch with them and see what you can work out. Framebags wouldn't work too well, but saddlepacks, handlebar bags and gas tanks don't need to be too customised.
I think what would making a touring shop stand out would also be putting spares on display as a "you need this". I'm not sure I've ever seen a bike shop with spokes on display - although they probably all sell them. Get people thinking about all kinds of spares and there are probably many sales to be made.
Books, maps, etc are good. I have a fantastic compact street directory of my (rather large) city, which I've never seen for sale in a bike shop - why not?
Consider freeze-dried food, jerky, museli bars...
And everything dan the man said.