ORIGINAL: Delta_V
Actually, Sabin, your first suggestion is probably the most practical....Kinetic impact weapons. All you would need is a large enough mass and the means to accelerate it and voila! All of the power of nuclear weapons with none of the radioactive fallout and the ability to conserve (I would imagine) hard to come by antimatter for those really nasty customers.
Anyone remember a novel called "FOOTFALL"? Basically elephantine aliens attack Earth. There ancient warrior code was if they got an opponent on the ground and held them down with their foot, there opponent would have to concede.
So, their method of planetary attack was based on the same theory. They'd tow in a astoriod and drop it on the planet. It would do serious, but not world ending, damage. They would then presume the race that owned the planet would concede.
