My all-time favorite meta-magic spell combination:
Feats:
Elemental Focus - Lightning
Greater Elemental Focus - Lightning
Spell Focus - Evocation
Greater Spell Focus - Evocation
Dazing Spell
Persistent Spell
Spell Perfection: Ball Lightning
At 15th level, cast a Dazing Persistent Ball Lightning which brings into existence 4 balls that you can control independently as a move action. Anyone who takes damage from just one of those Balls must make two saving throws at -8 or be Dazed. The Spell lasts 15 rounds. You can target one ceature with multiple balls if you wish. Its effectively a 6th level spell which means that at 15th level or higher, you can essentially cast it every major encounter.