[-Eidolon-]

Ah man, I spent wayyyyy too much time on this game back in the day. I used several of the ones you mentioned. Assassin/Elementalist was another, along with Elementalist/Red Mage for double cast. Sage/Alchemist was one of my most powerful, if I remember correctly. Oh, and a stereotypical Paladin/Fighter (or vice-verse) with Concentrate. Holy Blade was a one-shot every time.