Add this to your initialize function:
<script type="text/javascript">
function initialize() {
var map = new google.maps.Map(document.getElementById("map-canvas"), mapOptions);
// Resize stuff...
google.maps.event.addDomListener(window, "resize", function() {
var center = map.getCenter();
google.maps.event.trigger(map, "resize");
map.setCenter(center);
});
}
</script>