I recently bought an Android phone and my favorite app is called MyTracks which uses the phone's GPS to record where you've been. I mainly use it to keep a record of my cycling training rides. A similar app popular among cyclists is produced by Strava which integrates with their excellent website. However, their app did not seem to do a good job of acquiring and holding the GPS signal whereas I've had no problems with MyTracks. An added bonus of MyTracks is that it is all open source, giving me a chance to examine the innards of a well-made Android app.
A nice feature of MyTracks is that when I finish a ride the data can be easily uploaded to a Google Spreadsheet and/or Fusion Table. I decided to create a website that pulls your ride data out of the Fusion Tables and allows you to browse, share and annotate your rides. At first, I wanted to host the site here, but the functionality was quite limited by the constraints imposed by developing within Google Sites. Some notes here.
Instead, I decided it was a good opportunity to dive into more RubyOnRails coding. The source is here. See the README.md file for a list of the excellent web resources that I found useful in building the site.
And here's the site itself: http://johnwilde.us/ Get MyTracks for your phone, try it out and let me know how what you'd like to see added.