When one runs out of firebased spells... phantasmal killers do a nice job. Have you experiemented with the shadow adept prestige class yet? One of the guys in my last game got the idea from me, but roled an 18 (I allowed subraces) so he played a sun elf illusionist, put the 18 in int, which was raised to a 20. Took the feat spellcasting prodigy illusionist and picked up shadow adept at 6th level. Very nasty by 7th level with the phantasmal killer spell. He look the craft wonderous items feat as soon as possible, and at 8th level invested in crafting a headband of intellect +6 (by then his intelligence was naturally a 22, and 24 for spellcasting purposes due to his feats). Stack that with the 3rd level shadow adept abilities and and greater spell focus illusion, it unbalanced my game very very fast. He killed that archvillian of my campaign with a single phantasmal killer spell, at 9th level. LoL Some of my players are notorious for finding ways well within the confines of the rules for making rediculously powerful charaters, although the focus of my games is character development and political intrigue.