Frost Battlemage Armor is the strongest form of Armor you can acquire (as of V0.6.5) and is acquired from the mage entity, but in future updates this will change!
It is planned to have special effects when the whole set is worn, this however is not implemented yet.
Bone armor can be acquired by crafting it with; you guessed it; bones. It is a weaker form of armor than Leather but it can be a nice addition to a collector of armor sets to put on display and maybe in the future it can be placed on a magical companion; you'll just have to wait and see! To craft this armor simple go to a crafting table and you should see the recipes for the armor.
Rubedite armor, one of the older variants of armor released in one of the older updates. It is a basic armor type providing decent protection and can be acquired by smelting Rubedite ore found from mining in a furnace and using the ingots to make the armor. The tools are also the same process. (Go to a crafting table and you will see the recipes)
Soul armor, another older variant of armor released in an older update. It provides decent protection, better than rubedite and can be acquired by smelting Soul ore found from mining in a furnace and using the ingots to make the armor. The tools are also the same process. (Go to a crafting table and you will see the recipes).