I have just released KeyDragZoom 2.0.1. In this release, the visual
control remains above the veil pane so that you can turn off drag zoom
(after you click the control but before you start dragging) simply by
clicking the control once again.
With KeyDragZoom you can add the same type of drag zoom capability
that is currently used on
maps.google.com to your own maps -- except
that the implementation is more complete (supports tool tip help,
ability to set a cursor (crosshair is the default)). And, of course,
you can also trigger the drag zoom from the keyboard by holding down a
hot key (usually Shift, but can be set to Ctrl or Option/Alt).