Kinetic Bombardment: Basically, you just toss something really heavy down at the planet, and watch the nuke-level destruction without the unpleasant radiation! http://en.wikipedia.org/wiki/Kinetic_bombardment Grey Goo: Awful. A self replicating nanobot that eats everything. When you use it, it'd start growing after a while, then once it stops, the planet will be covered in dormant nanobots and the mineral supplies would be drained. Bioweapons: Dangerous, but they require a lot of research to make. Of course, if you're the sneaky type and have a good reputation, you could use them with no consequences. They'd just kill about two thirds of the population, unless a cure is developed before it can. If you help the planet with recovering, you might get positive reputation. And if you plant the bioweapon stealthily, no one will suspect you.
Here is a thought for this, what if the Grey Goo transfers the Resources to your ship, that way you wont feel so wasteful The kietic Bombardment would be awesome, send a Dwarf Planet into a bigger planet and watch the anarchy This are both good suggestions and could actually work to some dagrees
