If you download the latest version of Google Maps for Android you can now download huge areas to use offline. In the latest version of Google Maps for Android you can save up to six large areas.
To save an area you need to navigate to the area you want to download and select 'Make available offline' from the menu. You are then shown the size of the file you want to download so that you know how much space it will take up on your phone.
Via: Google LatLong