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Are there any spells that give decent bonuses to skill checks? Even something like a +10 bonus to the next check would do. The guidance spell just doesn't cut it...
The heroism spell (Sor/Wiz) adds a +2 morale bonus to skill checks.
The greater heroism spell (Sor/Wiz) adds a +4 morale bonus to skill checks.
The divine insight Spell (Cleric, lv 2, Complete Adventurer) grants up to +15 to a single skill check.
Glibness is the most extreme I know of off hand. This gives you +30 to your bluff for 10min per level. It only works when trying to convince somebody of something - nor for feinting etc. Still, this can have some pretty interesting and bizarre consequences when selling loot.
As for general skill check enhancement - what they said.
Wieldskill was commonly used in 3e, but was nerfed in 3.5e because there was little point in taking skill ranks in some skills when a low level spell is much better.
Divine Guidance (CAdv), Clr2, gives up to +15 to a single check, depending on caster level.
The WoTC website version gives a straight +20 without the caster level requirement... it is a horribly overpowered version of an already somewhat overpowered spell.