Geotags for iPhone is a good start
Geotags [App Store link] is a free map-based application for the iPhone. Its purpose is to keep a geographic diary of sorts, letting you mark maps with tagged information you'll want to explore again.
You can geotag your car so you can find it again, or a favorite hunting location, or a cave. I tested the app by recording some favorite spots in a nearby state park that were good photographic locations.
It's a bit like Places in iPhoto, but it is portable. You can add photos to geotags, or an audio clip (2 minutes max recording time for each clip) that describes it, and of course some written notes.
Once you have built up a database of tags, it can all be exported to Google Earth for sharing with friends, or just to use yourself.
I found the app is a really good start, but it feels more like a beta than a finished, polished program.
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