Here's my 100% success seat post extractor:
Gotta be REAL careful, wear hand/eye/body protection, mask any paintwork you want to preserve in case of spillover, have some vinegar on hand to neutralize any spills.... but I've done 2 seatposts and one stem this way, and it's a lot less sweat and potential damage to the frame. Dissolves aluminum and leaves steel alone. If you're going to do it, do your homework, this stuff is very dangerous if you get it on your skin...