In order to prevent blank page syndrome, starting with a very basic bestiary list.

I'll expand and refine as I go, but this will at least be a good jumping-off point.

Howlers - tusked super-mutant-like creatures that can let out a resonating howl that carries great distances. They use their howls to communicate and coordinate.

Grays - Aliens? Aliens.

Gotta have radroaches.

Zombies - need to decide between slow zombies and fast zombies, or to have both.

Ghost People - a la MY0, mutants with transparent skin and minor telepathy.

Robots - Protectrons and the like, as well as bigger, badder bots.

Skeeters - like Fallout's bloodbugs, but I did it first.