There are a number of Geocaching apps available for Android and most of them are targeted at the GC.com user. There are a few that support OpenCaching by design or by request (in my experience, if the developer lives outside the USA, the app supports OpenCaching).
This is in no way an all-inclusive list.
I looked at these applications because they are actively developed (meaning updated often, or at least on a regular schedule) AND I use or have used them.
You can get all of them from the Market for free, with the exception of CacheMate (more on that in the description below).
As I get new information or discover new OC-compatible applications, I'll update this post.CacheMate
$8 if purchased through the Market.
Visit the app home page and you've got a few different options for obtaining: direct download, purchase or Trialpay.
Direct Download: Free, but you'll be limited to using the phone's internal storage for databases, instead of using the SDCard.
Purchase: buy through esellerate with paypal or credit card and recieve a registration key (tied to your phone IMEI) to unlock SDCard usage.
Trialpay: you know how those work...sign up for netflix, or magazines, that sort of offer and get it the registration key once completed.
CacheMate had been around for a few years before making an appearance on the android platform (I had used it on my Palm Treo back in the day).
Multiple Database support (nice for keeping OC and GC caches seperate. I also like to keep different dB for my neighborhood, work neighborhood, etc)
Imports GC and OC gpx files perfectly
Builtin compass (some apps require a 3rd party app or plugin to provide compass/radar).
Log finds/dnfs via sms (textmarks) or to a file, keep track of travel bugs.
The interface could use an update, in my opinion -- OR it's perfect if you like simplicity and functionality
Screenshots (click to embiggen) [yeah, my gps had trouble calibrating. Usually the compass is green]GeoHunter or GeoBeagle
GeoHunter is a fork of GeoBeagle (but both projects happily give and integrate features from each other) and I'll be focusing on Geohunter here.
GeoHunter has done away with the "dog and bone" theme of GeoBeagle and also revamped interface that focuses on tabs, making access to navigation, description, cache list, etc available most cases w/ one touch.
Imports GC and OC gpx perfectly.
Log finds/dnfs via sms (textmarks - currently applicable to GC.com) or to a file.
One thing I have noticed about GeoHunter - the "view web page" option doesn't work. Opening the cache from geocaching.com is hardcoded in to the program, so when you touch the "view web page" button, it tries to open up a GC cache page that is completely unrelated to the cache. If you want to view the cache on an OC, you'll have to view it in the phone's web browser. [UPDATE 12/11/10]
"Attributes" are displayed as a log entry by "SYSTEM".
Screenshots, including the two different compass that can be used with GeoHunter - GPS or "radar" (click a thumbnail to embiggen):
Visit the project home page
for a more current version than what's in the Market.[UPDATED 12/23/10] OpenGPX
Another app that started on another platform (symbian) before appearing on android.
Lists all caches found in all GPX/LOC files (sorted by name or distance)
Uses WebView for HTML cache descriptions
Supports geocaching.com (single GPX and pocket queries), opencaching.de, opencaching.us, geocaching.hu, GeoToad, GCTour files
Cache Database Management] for managing caches with clients
Multiple cache database support (copy/paste, rename default database. I have one for OC and a couple region-specific GC PQs)
Shows the main information about each cache (info, description, waypoints, logs)
Extracts coordinates (Waypoints) from description and logs
Internal image viewer for spoiler images (filenames have to contain one word of the cache name or the cache code)
or GPS Status & Toolbox
activity for simple compass / GPS navigation
Radar view (context menu on Waypoints) - requires Radar
Google map / OpenStreetMap view (All caches, all waypoints of one cache, single waypoint view menu on Waypoints)
Detailed waypoint information (incl. distance and bearing to other waypoints)
Navigation to waypoints with AndNav2
Caching Tools (Calculator, Groundspeak en/decode, Caesar en/decode, Morse en/decode, Prime factorization, Text2Number, Roman numbers, Checksum, Sum Ascii, Vanity numbers). Calculation tool supports variables (a=5, b=a+2)
Online Search via bcaching.com (requires a free account at http://www.bcaching.com
Log geocaching.com finds via bcaching.com field notes
Screenshots, of course. Click to embiggen:Android Cacher
Android Cacher just received a big update - now several opencaching domains are supported .us, .de among others. The dev updated because I
left a comment in the Android Market!
With the latest update, Android Cacher can search for caches from the opencaching domain you specify in the application settings.
Some info (at least from the .us domain) doesn't get imported, but an email correspondence w/ the dev today will most likely result in another update (he had me send him some cache IDs from opencaching.us that get b0rked). Will update again soon with screenshots, etc.