best penetrating oil to free up rusty parts forum I just found:

http://www.rumcars.org/forum/index.php?topic=3649.15

Mentions a product that I've never heard of,
Worth Rostoff

I'm reminded of the only test of the common penetrants I've come across that Machinists Workshop magazine did, http://justacarguy.blogspot.com/2010/10/penetrating-oils-compared.html and the winner was a 50-50 mix of acetone and ATF

Another forum had some different things mentioned that I'll repeat here to get all the info in one place:
Royal Purple Synthetic Lube Spray,
GM or Dodge Heat Valve Lubricant,
Engage by Drummond American,
Zep 45NC

all from http://www.3wheelerworld.com/showthread.php/112706-Penetrating-oil-test

Everyone seems to agree that one of the best in Kano-labs Kroil