a d2 crusader using a dip into Bloodstorm Blade (I think that is the one that lets you turn a ranged attack into a line, if not it may be a maneuver) is probably the simplest one.
alternatively use astral projection (probably best done by a NightMare) to constantly duplicate holding bags and portable holes until you can lay them around the planet and let them all generate rifts to the astral plane.
[spoiler]If a bag of holding is placed within a portable hole a rift to the Astral Plane is torn in the space: Bag and hole alike are sucked into the void and forever lost. If a portable hole is placed within a bag of holding, it opens a gate to the Astral Plane: The hole, the bag, and any creatures within a 10-foot radius are drawn there, destroying the portable hole and bag of holding in the process.
[/spoiler]
The d2 crusader, even if it works (I believe it was disproved somewhere, but I'm too lazy to Google it out), wouldn't actually destroy the world, as the d2 crusader's attack is considered a Supertask (a task which cannot be completed). The d2 crusader will continue rolling and rolling and rolling and his turn will never actually finish. The game would actually require DM fiat to say, "Okay, you killed him. Move along."
Basically yes it is an infinite loop that has no exit and takes no actual game time. It doesn't mean it can't be completed only that it will have cycled an infinite number of times during that action. It is the same as the Omnificier redirecting damage back and forth an infinite number of times and then drowning himself to remove the damage. He technically can't break the cycle either. That is the problem with all infinite loops in any gaming system, they are infinite. It has been an accepted thought that you can choose to stop your action that the loop is a part of since game mechanics has no real way to exit.
Another choice would be to use an epic spell which can do whatever you want it to. You could even pull it off pre-epic if you can get into Illithed Savant as a Dragon Wrought Kobold. just eat some people for requirements and run with it.
besides we are talking about blowing up a planet, there will be some silliness involved in making that happen. With the number already discussed we could probably get a fireball or something metamagiced enough to do it too.