Guide:Crafting
There's currently a guide on Crafting by Invalesco on the game forum.
http://www.pathofexile.com/forum/view-thread/54003/page/1
Velkor has also got a spreadsheet for item mods that may be a useful reference for those intending to do crafting.
https://docs.google.com/spreadsheet/ccc?key=0ArsB7KohOhhpdHoyZzU2WVZZNXQxMDg4MVk1b0FGbkE#gid=1