This is the list from SHTT: Skaul's Hierarchy of Tips and Tricks [SHTT] [2.5] and generally you want to watch out for any item that has a Legend affix Elemental DMG%, Weapon DMG%, or other useful Legend or set affixes that are not rollable through Amethyst and Ruby. A list of all of them can be found here: Crystal Crafting Restrictions
One thing I learned in the Arena - you are always going to get your face slammed. Unless you are the top 1.