There are many routes to create powerful wizards, but I've been playing around with this idea for a level 10 wizard (as an NPC) for a bit and thought to share.
Take an evil, necromancy focused wizard, high int, some positive charisma and whatever else you feel like. The charisma is for the command undead ability. Then with the charisma leadership feat is an obvious optimization. For a necromancer a negative energy cleric is also a logical choice.
From here these two will kill and animate everything they see in sight. They can also create undead at higher levels and take control of those too. So assuming they combine efforts, between the two of them they can control 90HD worth of undead at level 10. At level 20 this will scale to 190HD worth. The effective cost of this army is just the HDx25gp so for a high level character it's minimal expenditure.
Now this wizard walks into battle with a small army under his command and he'll still have a full compliment of spells to use.
I'm sure that there are single characters out there which can deal with this wizard, but its quite a powerful concept none the less.
Removing leadership will still allow for 50HD worth of undead at level 10 and 100HD at level 20.
Though any sane GM will never allow this, it is by the book. :)
