http://mytracks.appspot.com/
http://googleblog.blogspot.com/2009/02/happy-trails-with-my-tracks-for-android.html

This is the absolute one needed app of all mobile apps, so hurrah!!

If you've got a phone that can tell you where you are at any given moment then why not give you the option to show you where you've been, how fast you've travelled, where you've got to. It's a diary in visual form.