Omitting those from Oriental Adventures, Dragon Magazine, Dungeon Magazine, Polyhedron and White Dwarf I've got the following on my Want List that could be considered Other Campaign Setting Creatures:
Al-Qadim
Desert Giant
Reef Giant
Melnibone
Giant Owl [from Gods, Demigods, Heroes] (not the regular Giant Owl)
Nihrain Horse [from Gods, Demigods, Heroes and Deities & Demigods]
Dragonlance / Computer Game
Huge Bat [from Dark Queen of Krynn] (much bigger and nastier than standard AD&D Huge Bat)
Faerûn
Denizen [from Waterdeep]
Nehwon
Death Coral
Gladiator Lizard
Ravenloft
Sentinel Bat [from Ravenloft Appendix I - Creatures of Dread]
Archer Skeleton [from Ravenloft Appendix III - Creatures of Darkness]
There's a whole bunch of other possibilities, but those are the ones I flagged for attention either because I found them interesting, for the sake of completeness (the Huge Bat is one of the few Dark Queen computer game monsters we didn't convert), or for reasons I have forgotten because it was so long ago.
The Huge Bat and Giant Owl are probably the simplest of the above possibilities, but I'm currently most tempted by the Archer Skeleton.