Somewhere someplace I have a dent puller kit that uses a solid stick of glue (like in a glue gun) with a hook inserted at one end.
1) Clean the panel thoroughly.
2) Heat the panel evenly using a hairdryer.
3) Apply the glue stick to the centre of the dented area and hold until it sets fast. Allow to cool.
4) Put some rope through the eye of the hook and pull until the dent (hopefully) pops out.
5) Heat the panel again to remove the glue stick.
I've not tried it yet so I can't comment on how effective it is!
Mark.