I am looking for mods that improve vanilla creatures, not add new ones, by giving them new abilities, etc. So far I've found http://oblivion.nexusmods.com/mods/36726/? and

http://oblivion.nexusmods.com/mods/40878/?.

Any other recommendations?

Perhaps you're looking for something like this: http://oblivion.nexusmods.com/mods/31882/? FYI you can always try the mod detectives thread if you're looking for mods. You'll get more help that way.

Thanks for the tip, shinobi, and the recommendation.