Clear Quartz & Amethyst together will help to amplify protection and protect accordingly. Blue Obsidian is another good one as is Carnelian. I also like the black stones as well, because they are quite handy, Apache Tear & Obsidian.... equally... but also its wise to mention Lapis Lazuli as well as that too has protective qualities. It is however what you are drawn to work with, generally, overall, what calls out to you to work with as to what you are comfortable with. :) There was one stone recently that I came across which is good for psychic attack, I will have a look in my email, because I'm sure that there was another stone that I came across which I got recently that is good for protecting up against negative psychic attacks. I fairly certain it may have been Obsidian, though.