For Evil I would buy the following:
Armory (40,000)
Fire Miracle (60,000)
Ranged Armory (70,000)
Lightning Miracle (90,000)
Volcano (1,000,000)
Punishment Spike (10,000) - putting these around your Volcano will allow it to charge up faster.
Also get the following "Good" things, they come in useful:
Shield Miracle (30,000)
Siren (200,000)
If you get close to taking a town by impressiveness, you might be interested in the following:
Temple (40,000)
Amphitheater (200,000)
I didn't see much point in getting the Siege Workshop, I used my creature to knock down walls. Things like the Prison and the Torture Pit didn't show me much either. I thought the Hurricane and Earthquake miracles didn't have the precision of the Volcano.