The Great Revenance spell from City of the Spider Queen is unfortunately quite prohibitive. It requires an Undying Temple or suitable other undead construct with a large negative energy supply. Even then, it only creates Revenants which, aside from lasting a mere six months, have an unfortunate tendancy to attack those who killed them (barring special artifact-level persuasion). And that 'person who killed them' is most likely you if you call yourself a necromancer of any note.
While the aforementioned wraith method works, I myself prefer shadows or specres if one has the means to control them. Their attacks have the benefit of not allowing victims a saving throw to avoid death. At a low 3 HD (modified up to five from turn resistance), mobs of shadows also provide very good protection against troublesome would-be adventurer heros.
