I\'ve been trying to get pretty charts to work in GWT on our internal network.
Playing around with GWT-Ext\'s charts is nice, but it requires flash and is really mes
Google's charts actually come in two flavours, and one of them does not require interaction with Google's servers - so should satisfy your needs.
Google Image Charts is the API you are thinking of, which is an API on Google's servers that returns images.
Google Interactive Charts is a client side javascript API that renders entirely within the browser: Google Interactive Charts
Google provides a GWT wrapper for the interactive charts: GWT Visualization API
It's not all rainbows and unicorns and you can find chart libs out there that make nicer charts, but it's pretty solid, works on all major browsers and we've been using it successfully for quite a while.