5th:
Bewildering Mischance (Single Target sadly, but roll twice on almost everything and take the lower of the two on failed Will save - Complete Champion)
Curse of Petty Failing, Legion's (AoE -2 to attacks and saves AND has no save against. SR applies, but no save still dood! - Miniature's Handbook. The single target version is only 3rd if you aren't fighting mobs)
Mana Flux (Fuck over the eventual 'god' boss with an unavoidable 20% spell failure chance. Not arcane spell failure, but just plain
spell failure chance. Yay it affects EVERYTHING! Also works on spell-completion items like scrolls. It also says if the creature is already affected by a spell failure chance, to check against each source separately. See if you can get away with stacking this field :3 - PHBII)
Flame Strike is never not useful IMO.
Monstrous Regeneration (Actual regeneration, like trolls do. Magic of Faerun)
Wall of Ooze (The damage is low, but it can paralyze and eat creatures to make itself stronger! It autokills in 1d6 rounds if it paralyzes a creature <3 - Book of Vile Darkness)
4th:
Delay Death (Temporarily immune to dying from raw damage? *shrugs* - Spell Compedium)
Pronouncement of Fate (There's alot to this spell depending on circumstances but straightforward it inflicts a -4 to most rolls on a target and, circumstances pending, a % chance of the target losing all of its actions for the duration of the spell. Best case scenario is 50%. If the offense the target has commited affected you personally, they can only at best reduce the % to 25% to lose all their actions for the duration. It's a beautiful, if slightly convoluted, spell - Heroes of Horror)
Stars of Mystra (1 star per 3 lvls you can shoot as a swift action at specifically evil creatures to make them save or lose a 4th level spell either prepared or per day if spontaneous. If no 4th, it goes to 3rd, and then next lower if none of those left and so on. Be nice if went higher than 4th, but still, it lasts minutes per level and what else do you use Swift actions for currently?
)
Yeah Clerics ain't got much decent stuff in 3rd and below that aren't buffs for me to keep looking >.>