If you are just looking to get rid of them, Banishment and Dismissel will send them back to their home plane, though higher powered outsiders can usually find a way back pretty easily. If you would rather they not teleport/plane shift as much as they do, Dimensional Anchor will keep them around. Otherwise, most outsiders are heavily aligned on one or both axises, so I would look at all the alignment based spells (Prot. from evil, Order's Wrath, Holy Word, etc.) and try to keep straight what you expect to be fighting (Devils are LE, Demons are CE, etc.)
|
Knowledge: Planes is also very useful to know what they're resistant and immune to, because lots of outsiders are immune or resistant to several things.
Make sure to stock up on cold iron and silver weaponry, preferably enchanted.
If you want to use energy attacks, make sure you can do several different elements, because otherwise you might be stymied by aforementioned immunities and resistances; most outsiders are immune to 1-3 and resistant to 1-3 energy types.
Magic Circle vs. Alignment is very useful for creating a safe zone that they can't attack in melee. They can still attack at range, but it'll stop them from harassing your pet wizard in melee. (However, don't forget that it also stops you from engaging them in melee, unless you have really good reach. If you force a barrier spell against a creature, the barrier spell pops. There's nothing wrong with a ranged attack cleric though.)
This is not a spell or magic item, but you could also take the feat Alignment Channel--pick vs. evil outsiders to fight demons, devils, qlippoths, etc. This would allow you to apply the effects of your channel energy ability against these creatures. Now, channel energy isn't massive amounts of damage, but you don't have to prepare it either. You could also take Channel Smite + Alignment channel if you are a melee oriented cleric.
Other advice:
- Take Knowledge (Planes) -- this is the skill your character needs to help learn the differences between and weaknesses of different outsiders.
- For weapons, holy weapons and/or evil outsider bane weapons are good
- For spells, what Domingo said. Holy Word is especially awesome once you're high level enough to use it.
- If you're low level, make lots of holy water--doesn't do massive damage but you can do it at first level and you can always have it around in a pinch. You could use it with a battle aspergillium as well (from APG).
- Other low level stuff -- keep around silversheen and, when you can get it, a cold iron weapon, and either prepare magic weapon or keep around oil of magic weapon. The last is important for low levels because usually less powerful outsiders have their DR resisted by a magic material OR magic, so just a magic weapon can suffice.
- Finally, don't overlook best low level anti evil outsider spell -- protection from evil. Beyond the AC bonus it helps keep outsiders from influencing you mentally and can provide protection from summoned evil creatures (like fiendish creatures summoned with the summoned monster spells).
- Generally speaking, outsiders usually have a good to hit and AC and spelllike abilities, so party buffs are always good -- any you have on hand. Make it easier for the PCs to hit, harder for the outsiders to hit, and easier for the PCs to save versus the outsiders' special abilities.
Also as a small note, fey are not outsiders. :) They are their own monster type. Best way to deal with them is buffs versus enchantments and cold iron weapons. You can't banish fey of course because they are natives to the prime material plane. Also many fey are tricky but not belligerent, so find non combat ways of appeasing them.