I recently completed work on an iPhone app for warmshowers.org. If you're unfamiliar with warmshowers, then visit warmshowers.org to learn what it's about.
The app lets you visualize on a map the location of "available" hosts in your vicinity, mark them as favourites (for easy retrieval later), and get in contact with them. You must have an account on warmshowers.org to use this app.
You can download and try the app by visiting the App Store and searching for "warmshowers", or by clicking this link:
The app is 100% free. Enjoy!