since gez posted the mystara compendium contents, i will throw in the planescape compendiums and boxed sets. i meant to do this awhile ago, but never got to it. i'm sure there are several (maybe even lots) that are in books and i missed em or forgot em, so correct me as needed.
PSMC1 - Planescape Monstrous Compendium Appendix I, 1994
Incarnates (DR193)
Imp, Mephit (Radiant, Lightning, Ash)
PSMC2 - Planescape Monstrous Compendium Appendix II, 1995
Demarax
Dhour
Eater of Knowledge
Eladrin, Bralani (Lesser)
Eladrin, Coure (Lesser)
Eladrin, Noviere (Lesser)
Eladrin, Shiere (Lesser)
Eladrin, Tulani (Greater)
Ghostlight
Incantifier (Sect)
Merkhant (Sect)
Observer
Prolonger
Quill
Rager (Sect)
Razorvine
Reave
Rilmani, Argenach
Rilmani, Plumach
Shadowdrake
Spellhaunt
Spider, Hook
Sunfly
Sword Spirit
Tanar'ri, Bulezau (Lesser)
Tso
Wastrel
Wraithworm
PSMC3 - Planescape Monstrous Compendium Appendix III, 1998
Animental
Archomental (Good) (Ben-Hadar, Chan, Sunnis, Zaaman Rul)
Bzastra
Chososion
Darklight
Devete
Dharum Suhn
Egarus
Entrope
Facet
Garmorm
Homunculous, Elemental (Breather, Skin)
Klyndes
Magran
Menglis
Nathri
Ooze Sprite
Opposition
Phirblas
Primal
Quasielemental, Negative (Ash, Dust, Salt, Vacuum) (DR128);
Quasielemental, Positive (Lightning, Mineral, Radiance, Steam) (Lightning-MM2, others DR125);
Ruvkova
Scile
Shad
Shocker (Contented One, Sojourner) (Contented-FF, Sojourner-MC14);
Sislan
Suisseen
Tsnng
Ungulosin
Vacuous
Wavefire
PSCS - Planescape Campaign Setting, 1994 (PS boxed set)
Dabus
Nic'Epona
PoCh - Planes of Chaos, 1994 (PS boxed set)
Asrai (DR191)
Chaos Imp
Murska
Ratatosk
Viper Tree
PoL - Planes of Law, 1995 (PS boxed set)
Busen
Gear Spirit
Moigno
Parai
Rust Dragon
PoCo - Planes of Conflict, 1995 (PS boxed set)
Aeserpent
Buraq (MC13);
Delphon
Ethyk
Gautiere
Linqua
Ni'iath
Quesar