I recently wrote a very simple addon to Dwarf Fortress: a pair of text files that add a significant amount of creatures to the game. Simply download the .zip file, and extract it (or copy & paste the files into your raw\objects\ folder). The two files are creature_pack.txt and body_pack.txt.
Feel free to use them for any mods or additions you feel like doing.
http://teldin.wikispaces.com/space/showimage/creature_pack.zipHere's a full list of every creature included:
aboleth
ankheg
assassin vine
avoral
basilisk
blink dog
bugbear
centaur
chimera
cockatrice
red, blue, green, white, black dragons (megabeasts)
island turtle (might be buggy.. tried to use a green wagon thing)
dryad
dark dwarf
dark elf
formian
frost worm (semimega)
blue, green fungus patch
gargoyle
ghoul
fire giant
frost giant
stone giant
griffon
hippogriff
werebear
wererat
manticore
naga
bone naga
nymph
gelatinous cube
green ooze
giant owl
owlbear
pegasus
purple worm (megabeast)
remorhaz (megabeast)
roc
sahaguin
salamander (flamey lizard snake-men)
stirge
red stirge
will-o-wisp
wyvern
xorn
winter wolf
baboon
rock troll
bog troll
pig (domestic, trainable)
chicken (domestic)
field mouse
rabbit
weasel
sheep (domestic)
coyote
zebra
wild boar
rhino
blind salamander
white striped lizard
rock lobster
ocean lobster
cave shrimp
free-tailed bat
leaf-nosed bat
ghost bat
vampire bat
evening bat
phoenix
hieracosphinx
scorpionman
Also, yes, most of them are from D&D. You can actually find a list of them at this lovely resource:
http://www.d20srd.org/indexes/monsters.htmAlso note that if you already have mods installed, some of the creatures may overwrite them and you'll get all kinds of silly bugs, like wizard dwarves and mermaid megabeasts.