General:
* Beings
* Organisms
* Living things
* Animals (if referring to non-human animals)
* Life forms
* Inhabitants (referring to creatures in a specific place)
More specific:
* Animals (for non-human animals)
* Beasts (for wild or ferocious animals)
* Monsters (for mythical or terrifying creatures)
* Insects (for small, invertebrate creatures)
* Birds (for feathered creatures)
* Fish (for aquatic creatures)
* Reptiles (for cold-blooded, scaly creatures)
* Mammals (for warm-blooded animals with fur or hair)
Informal:
* Critters
* Things
* Guys
The best choice will depend on the specific context of your writing.