I'm currently playing a Transmuter focused on buffing and battlefield control. Are there any good spells from either the APG, UM or UC that you'd recommend or does the Core book pretty much have the best stuff?
Crafter's Fortune (1)(APG) - if you like crafting.
Enter Image (3)(APG) - lets you "possess" an image of you for scrying and such.
Glide (2)(APG) - like Feather fall except you can move horizontally as well.
Gravity Bow (1)(APG) - helps with damage from archery.
Liberating Command (1)(UC) - immediate action help escape from grapples.
Monstrous Physique (3)(UM) - if you like polymorphing.
Twisted Space (2)(UC) - target attacks random adjacent character instead of initial target.
What are your opposed schools? UC has the communal spells, basic buffs that you can divide the duration amounts the party.
Protection from Alignments, Protection from Energy, Resist Energy and so on
Oppositions are Enchantment and Divination.
I'm currently playing a Transmuter focused on buffing and battlefield control. Are there any good spells from either the APG, UM or UC that you'd recommend or does the Core book pretty much have the best stuff?
Well, I'm drooling over Selective Spell metamagic, which you have to be 10th level to take, but wow I'd really like to drop Black Tentacles and have my allies ignore the effect. Or Cloudkill. Truly 'friendly' fire!
Taking a look over the feats of the three books:
The APG's Spell Perfection seems handy but a steep requirement of three metamagic feats. Speaking of which, Elemental Spell seems like it may be handy but situational. Selective Spell looks like it would also be handy for blasting or any AoE spells.
In UM Spell Specialization isn't too bad and the Greater version seems interesting as well. Not sure I'd want to take them though. Uncanny Concentraion might be useful as well but a mere +2 makes me wary for the cost of a feat. Echoing Spell looks really nasty.
Nothing in UC strikes me as worth it.
YMMV but i like the look of the feat destructive rispel frum uc, having the ability for my dispels to stun even for one round is gravy. Bbeg's by 11th level tend to have at least some buffs, tossing out an early dispel, stripping his haste or resist energy or well you get the idea then causing him to drop what he's holding and drool like an idiot for a round, or even if he passes sickened for a round just makes buff shearing more worthwhile.
I can see how that could be worth taking later on in levels.
I don't know if you'll be facing a lot of undead in your campaign, but consider swapping out necromancy for enchantment, or even abjuration for enchantment. Both schools have few 'always prepped' spells, and can easily be put on a scroll for later use. Enchantment on the other hand has a wide range of powerful spells, especially at later levels. Even spells like Sleep are combat enders at low levels.
We're level 3 right now and undead have been pretty reoccurring so far and I'm sure they'll be back in the future. Unfortunately the choices have been made so there're no takesy-backsies.
Reach Spell is very handy for a buffer -- you can use all those touch spells on people far away. Or you could extend the range of your offensive spells (extending "close" to "medium" is very nice)