Google has released a new application called My Maps Editor by Google for Android Market, that let you create, edit, share, and view personalized maps on your Android powered phone synchronized with the My Maps tab on Google Maps. Create a map on your desktop computer using Google Maps and then take it with you on the go and update it on location. My Maps Editor by Google supports full editing functionality for markers, lines, and shapes on maps, plus the ability to mark your location using GPS or attach a photo directly from your phone. Your maps are automatically synchronized with your My Maps on the web. Check out this tour of Google Mountain View.
More info: Google LatLong blog