Feel your pain. I am working through my first stuck seat post (aluminium post stuck in steel frame) and it is driving me bonkers. Thus far I've tried:

1. Regular old oil soak. That was naive.
2. Liquid wrench. No go.
3. PB Blaster, through the top, through the water-bottle braze ons, through the bottom bracket. Not even a twist.
4. Big wrench on the saddle clamp. It slipped a bit on twisting--but only the clamp not the seat post.
5. Seat clamp/post in bench vice and rotate. Just slipped the seat clamp around and around in the seat post.
6. Crc-Freeze off from both ends + big pipe wrench (seat post is already trashed). Still haven't rotated it a bit.

So I guess the only options left are 1) ammonia soak 2) dry ice and 3) a hacksaw.

Other idears?