In terms of elements, I have heard that a form of nitride is the hardest, nearly 80 times harder than what was considered the hardest element till now, namely diamond. This form of nitride is said to be somewhat structurally akin to a diamond but differs in its composition of atoms.
In terms of materials, earlier this year a wonderful discovery of a hard material was made by scientists & reported by USA Today. As per their research, a limpet, which is a resident of the sea, has got incredibly strong teeth. This is due to it having fibers made from a mineral called goethite. Though thin, these fibres hold a lot of strength, so much so that the fibres are said to be stronger than the silk ones which a spider weaves for its webbed home. What's more, the goethite fibres can withstand even greater pressure than those uses for Kevlar vests. Just imagine the incredible possibilities of this hardest material - the structural bodies of ships and aeroplanes could incorporate it. Wow!