This is one I've had floating around for a while, and may even do someday...
The Pulp Sci-Fi army! Flash Gordon and Buck Rogers, Mongo and Barsoom, rayguns and rocketships! While I'd probably do mine in color, I think it would be a hoot if someone painted them up to look like they were on black & white film.
The basic army will be human/alien troopers with fancy rayguns for the various blasters/dark lances and so on, with hover skiffs/rocketships for the Raiders and Ravagers.
Some example miniature possibilities:
http://www.pulpfigures.com/catmain.php (especially the US Rocket Corps and the Weird Menace section)
The Hero (Archon/Dracon)
-Extraordinary swordsman, raygun, capable of amazing feats.
Mad Scientists (Haemonculi)
-Not-quite right folks with even more fantastic weaponry than the rest of the force.
Royal Guard (Incubi)
-Elite sluggers on loan to The Hero.
-Tridents, nets, bad attitudes.
-Many attacks pass right through or bounce off harmlessly. Creations of the Mad Scientists.
Red Wolves of Zongor (Warp Beasts)
-Semi-tamed fauna from the wilds.
Troopers (Warriors/Raider Squads)
-Humans/aliens with rayguns. Sprinkle species, skin colorations and uniforms to taste.
Rocketpack Troopers (Scourges)
Rocket Gunship (Ravager)
TOBOR 2000 (Talos)
-Another creation of the Mad Scientists.