So, on Wikitravel, we have various "Expeditions", kinda like Wikipedia projects, for very specific projects within the travel guide. One of the Expeditions we just started is to identify and list related projects, and explore ways to cooperate with them:
http://www.wikitravel.org/article/Wikitravel:Fellow_Traveller_Expedition
Obviously, one of the main projects we'd like to cooperate with is Wikipedia and other Wikimedia projects. We use the MediaWiki software that runs Wikipedia, and we've learned about how to do our site from how Wikipedia works. I think we're all grateful for the software and the example, and we want to give back whatever we can.
We've got a page going about cooperating with Wikipedia here:
http://www.wikitravel.org/article/Wikitravel:Cooperating_with_Wikipedia
(Thanks to Stephen Gilbert for the original ideas). If you've got some suggestions, please feel free to add them to that page, or to the talk page, or respond here, or what have you.
Thanks,
~ESP