Are all books allowed? Because a human cleric with midnight metamagic, extend spell, and two alignment domains (chaos and evil?) can 1x/day summon an LG/CG/LE/CE critter that lasts for 6 rounds at level 1. That ain’t bad.

If fluff doesn’t matter, warmage gives you the boom boom. Versatile Spellcaster let’s you get more boom boom.