This is pretty much common knowledge, as everyone knows there will be many alts and re-rolls in Cata powerlevelling professions and everyone is probably stockpiling materials right now.
I just wanted to share how I find out what to stockpile. I've based my list on the following site:
WoW Professions | 1-450 WoW Profession Guides
Read through all guides and buy all the recipes (both limited supply and normal) you will find in the guide. After that farm or buy all materials you will find in the text. After the cata comes out, auction the recipes and list materials in AH in stacks as big as stated in the guides, i.e. if the guide says you will need 17 eternal waters to level this prof. just list stack of 17 eternal waters. That way you can set higher price per item and your stack will still appear before the 20 stacks.
BTW I've been setting the exact stacks of profession powerlevelling items after every patch for nice extra profit. Same works with events like Children's week, when you could list 3 mageroyals for 30g even when someone was selling 20 for 50g.