Thanks, found it on perltk.org
For anyone else who wishes to know. The tags to bind are 'Configure', 'Map', and 'Unmap'.
The Configure event is fired any time you move or resize the window (this includes maximizing). The Map event happens when you un-minimize a window, and Unmap happens when you minimize the window.
An example:
use Tk;
my $app = new MainWindow;
$app->bind('<Configure>', sub{ print "configure"; });
$app->bind('<Unmap>', sub{ print "Unmap"; });
$app->bind('<Map>', sub{ print "Map"; });
MainLoop;