- ESRI has a free ArcGIS mobile app for iOS and Android that allows you to access maps created on ArcGIS.com. This app continues to have increased functionality and its future looks bright. ESRI has a few other apps geared towards specific topics, i.e. business and health.
- iGIS is an interesting app that I hope to use more. Right now, it is free to download.
- Geograph apps provides a relatively low cost way to view to geologic information for various states.
- A Google Earth app with related imagery also exists
Many other GIS-related apps, even if just data viewers, are popping up: from flood plain apps to earthquake information. There are also many GPS and navigation apps ranging from a few dollars to some of the most expensive apps you will find anywhere.
Lastly, both iOS and Android Development kits are free or low cost. ESRI and Google also offer ways to tap into their maps and map services (for free and fee-based) to bring geospatial information into an app that you create!