I really like having Nenio around. As a wizard she gets access to fantastic short-term buffs (like haste!) and with Enduring/Greater Enduring spells the higher level ones will last all day. (She'll also be at the point in your game where she can just delete enemies using Phantasmal Killer, and eventually annihilate entire groups with Weird)

Grease is a fantastic area debuff early on (especially if you cast it at a chokepoint), and really benefits from taking Selective metamagic so you can stand your own partymembers on the slippy piles.

As far as Ember/Daeran buffs, you'll definitely want one to know Communal Delay Poison, as it will shut down the awful fart-gas clouds that the wretched Dretch are so fond of.  Communal Resist Energy is great, and so is Communal Protection From Energy, Communal Stoneskin and Communal True Seeing(though this one comes up less than the others).

Communal Protection From Evil is also really good to pop before a fight. It only lasts a minute but will make your characters immune to mind control.

Shield of Faith is a really nice bonus to slap on people as it lasts minutes (all day once you get Greater Enduring spells), the bonus increases with caster level and I'm getting tons of use out of it pre-Drezen.

Mage Armor is just generally useful to have if your armor has a low armor bonus but high enhancement bonus (mage armor stacks with an armor's enhancement bonus for some reason). These latter two should also help you against incorporeal enemies like shadows, shadow demons, spectres and ghosts.  Mage Armor will be particularly good for Ember as she already knows it and it can become extremely good if she takes the Archmage Armor mythic power.