I think I have come across the best method if you do not want to save the seat post. I have removed about 10 using this method and they are all very stubborn and two were almost impossible.
First I drill about a 3/16 or 1/4 hole through the seat post about an inch from the top. The drill should go through the entire seat post in a perpendicular fashion.
Next I take a disposable nut and bolt and thread it through the hold having the head on one side and the nut on the other.
Now I take and soak the area with wd-40 or any light penetrating oil. From the top take a regular hammer and hammer the seatpost in just a smigen to break any bonds, the bolt will keep it from going all the way in should it loosen up and this happened 4 times to me where I had to do no more work.
Now put the whole frame in a bike stand and turn it up side down. Take a claw hammer or claw crow bar and place it behind the bolt head as if you were pulling a nail. Once that is in place then take another hammer and strike the first hammer head to move the seat post out of the frame. The hardest one I ever did broke 4 bolts and took a half hour but this method never failed. I have had 100% success.
Good luck
Ray Homiski
Elizabeth, NJ