I just collected these guide apps and PDF downloads, I thought you may be interested. Here's the list:

ArrivalGuides - http://www.arrivalguides.com/en

Departures (AMEX)/Ultimate City Guides - http://www.departures.com/articles/apps

In Your Pocket - http://www.inyourpocket.com/static/downloads.html

Like A Local Guide - http://www.likealocalguide.com/

red|guide (Austrian Airlines) - http://www.redguide.at/mobile/

TripAdvisor - http://www.tripadvisor.com/apps

Triposo (Turkish Airlines) - http://www.triposo.com/

WikiSherpa.com - http://www.wikisherpa.com/

Sure, the scope and quality differs greatly, I guess a good check is to look up your home city/a city you are quite familiar with.

Feel free to supplement the list with your additions, maybe to make it a Thread Wiki or something.