I am doing Geography with my kids at the moment and obviously we use Google Maps quite regularly.  I recently discovered ScribbleMaps and now use this as my default Google Maps application as it offers everything that Google Maps does but has a handy little tool kit overlay that allows me to scribble, annotate, type or whatever I would like to do over the top.  That is as simple and as complicated as ScribbleMaps is but it's pretty cool nonetheless.