
Dragonsong |

there is a teamwork feat in the apg where 2 casters standing beside each other give CL bonuses.
the elf racial ability
human or dwarf cleric alternate favored class option boosts CL vs outsiders
then spell penetration and greater spell pen feats.
not sure of any spells unless your group allows lower resistance from the spell compendium, but that is sure not core/APG.
unless you are looking for boosts to CL for something other than overcoming SR.

meabolex |

You can boost your CL checks by boosting your caster level. There's a few ways to do that. . .
Items. . . Orange Ioun Stone, Bead of Karma from the Strand of Prayer Beads, moon circlet, etc.
There's a nice alternate bard class "theme" called the Magician that gives a caster level boost.
Halflings have an alternate race feature that boosts caster level for movement spells. Gnomes have one for fire spells. Elves have a racial ability that boosts light spells.
Death Knell increases caster level.

Prawn |

There's a nice alternate bard class "theme" called the Magician that gives a caster level boost.
I looked it up, Magician. It says "A magician gains the following types of bardic performance." and then lists Dweomercraft, Spell Suppression, and Metamagic Mastery.
Are these in place of or in addition to the other traditional bardic performances like inspire courage/greatness/death dirge?
Seems a bit anemic if a bard has to give up all of that other stuff just for three performances.

meabolex |

Seems a bit anemic if a bard has to give up all of that other stuff just for three performances.
Depends on the party composition. If you have all casters in your party (like bard, inquisitor, wizard, cleric), then it's pretty cool. Yeah, there's not so much synergy when your party is all fighters and rogues.