I would love to see more creatures in this game. Here are some I think would be cool and really add more variety in the game...
Barren/Deserts:
Giant Scorpions (would love to see these, clash of the titans anyone?), Sand Worms, Giant Ants, Cyclopse
Swamps:
Giant Snakes and other reptiles such as a Crocodile
Forests:
Ghosts, Giant Caterpillas and Centipeades, Panthers or other big cats, zombies
Snow:
Ice Giant, umm help me out with the snow creatures
Water (would love to see this):
How about a giant octopus or squid or other sea monster that can attack your transport?
Anywhere creatures:
Skeletons (these should absolutely be in), Giants (ogre is similar though, maybe these can be even bigger), Bone Dragon, Rats, Wearwolf, Grim Reaper, Minotaur
Well, these are all I can think of for now. COME ON PEOPLE ADD SOME MORE!
Ideas seem like they can be endless with this game as far as creature types go. How about some cool D&D style creatures. Heck even check the creatures over at Spore, that gives really good ideas.