I keep seeing descriptions (e.g.
http://ww2010.atmos.uiuc.edu/(Gl)/guides/mtr/fw/fric.rxml) of winds
blowing parallel to isobars. Yet surely this is not physically possible?
The only force driving the wind is the pressure gradient force. The
Coriolis force always acts perpendicular to the direction of movement,
so it cannot do work--that is, change the kinetic energy of the wind in
in any way.

Look at it this way: the pressure gradient force is always perpendicular
to the isobars. The Coriolis force is always perpendicular to the
direction of the wind. So when the wind is moving parallel to the
isobars, you have both forces acting perpendicular to its motion,
leaving _no_ force acting in the direction of its motion. So what's
keeping the wind moving against the drag of the ground?