Well it seems that as far as handles go the big five seem to be G-10,micarta,carbon fiber,titanium,aluminum.Then there are your natural materials.I think it winds up being a matter of preference and intended pupose for the knife when choosing a handle material.Some materials have better attributes or strong points in certain areas.So lets say you need a extremely chemical resistent handle,certain materials would be better suited for the purpose.The above listed though are the major popular materials at this point in time it would seem.