The following spells buff allied spellcasters:Arcane Concordance: Bard/Skald only, Lv3- +1 DC and free metamagic of caster's choice to allies' spells cast within radius of you while duration lasts
Collaborative Thaumaturgy: Almost all casters, Lv3 - immediate action to apply free metamagic to a spell being cast, selection increases per ally casting it, but the otherwise adjusted spell level cannot be above the caster's highest spell level
Spirit Call: Druid/Hunter/Shaman only, Lv1 - +1 CL and +4 insight concentration to all spells (not just allies') on your spirit magic list (excepting wandering spirit) or domain spell list to spells cast within radius of you while duration lasts
Font of Spirit Magic: Shaman only, Lv3 - +2 sacred/profane (alignment determines) to CL checks, concentration checks (yes, that's redundant), and DCs of allies' spells belonging to your spirit and wandering spirit list cast within radius of you while duration lasts
Sharesister: Cleric/Oracle/Warpriest/Witch only, Lv3 - Take 1 negative level to give ally of same gender +1 insight to CL and DCs of all spells. At CL11, you can choose to take 4 negative levels to give ally of same gender +2 insight to CL and DCs of all spells. At CL17, you can choose to take 6 negative levels to give ally of same gender +3 insight to CL and DCs of all spells. Effects that prevent or remove negative levels immediately end Sharesister spell. Negative levels from multiple castings stack. FYI:
Dhampir and
Shabti races can stack negative levels while ignoring their penalties, and the
Death Ward spell, cast afterwards, will also let you ignore penalties from negative levels.
Grand Destiny: Alchemist/Arcanist/Mesmerist/Sorcerer/Summoner/Wizard Lv5, Bard/Medium/Skald Lv4 - 10 min/lvl buff that is expended in 2 uses to give +4 competence bonus to any attack roll, caster level check, saving throw, or skill check. At level 12 and 15, add an extra use.
Rune of Rule: Arcanist/Bard/Occultist/Skald/Sorcerer/Witch/Wizard Lv2 - 1 day buff (cannot be applied to self) but 1 round duration when activated as swift action which gives +3 to will saves and +1 to save DCs of language-dependent effects or alternatively raises DC of a single charm spell by 1.
Aside from that there are a number of
teamwork feats that apply to spellcasting.
Class features:Variant channeling (can be done by any divine caster): Magic gives Channel Bonus to CL checks and concentration checks until end of your next turn. Secrets gives CB to Sense Motive checks, CL checks, divination save DCs until end of next turn. There are a number of Harm effects that penalize saves too.
Arcane subdomain: Standard action, gives +1 bonus to CL or DC (caster's choice each time they cast) for arcane spells cast within 15foot radius until end of next turn. 3+Wis uses.
Coven abilities (Witch's Coven hex, Sorcerer's accused bloodline arcana, Coven-touched changeling racial feat) let you use aid another to give allies +1 CL for 1 round. Stargazer PrC 1 gives witch hex of choice (no dead levels)
Witchguard Ranger - Defend Charge: 1/day (+1 use @ lvl4 and every 3 levels thereafter), Move Action to give adjacent spellcaster +2 Dodge to AC & +2 Circumstance to Concentration (+2 at lvl 5 and every 5 levels thereafter). Bonus lasts a number of rounds equal to Ranger's wis modifier.
Pathfinder Chronicler PrC 9 - Inspire Action: Expend 1 round of bardic performance to give an ally an additional standard action. As a bardic performance action, this action can be done as a standard action, move action (at 7 levels of bardic performance), and a swift action (at 13 levels of bardic performance). Pathfinder Chronicler advances bardic performance at -2 levels, so at level 15 you can use it as a swift action as well. (If you advance from
Dawnflower Dervish Bard, you start with move action and get Swift at bardic performance level 10, giving you Swift Action inspire action at level 14 immediately.) Anyway, tons of standard actions for your party's spellcasters. If you use
Experimental Spellcaster feat from Ultimate Magic's Words of Power rules to gain the Accelerate effect word, you can have an extra move action. Bear in mind regular Bards/Skalds can also give standard actions with the Heroic Finale (Lv5 standard action, ends performance) spell. Combined with Metamagic Rod (or
Spell Perfection) with Quicken metamagic and The Dance of 23 Steps masterpiece performance (starts as free action), you can give 2 standard actions to your target of choice as well.
Bard 8 or
Skald 10 (sooner with
Doomharp): Enemies within radius (30 foot default, higher with feats or Doomharp) are automatically shaken, no save (-2 to all saves, attack rolls, skill checks, and ability checks) until performance expires or they leave radius.
Void variant school specialization - Expose Weakness (Wizard, School Savant Arcanist, or just School Understanding arcanist exploit): 3+int uses/day. Standard action. For 1 round, target creature takes 1/2 your CL as penalty to AC and all saving throws (no save).
Misfortune hex (Witch class, Shaman class, Stargazer PrC 1): Standard action. 1 round. Anytime the targeted creature makes an ability check, attack roll, saving throw, or skill check, it must roll twice and take the worse result. A Will save negates this hex. Duration can be extended by 1 round for each move action spent on Cackle (for Witches) or Chant (for Shamans) hex.
There should be a bunch more stuff I missed.
