I was thinking a Vampire Dwarf army would be kind of cool, the fluff being that a Vampire bit a Lord who went back to his hold and feasted and turned his whole clan. Or maybe just a unit of Zombies that was modeled up using all the various races painted up zombie style would give the impression that it was raised from the all the fallen foes over the centuries.. Just a couple ideas I had.
I have a mixed VC army. The idea for me is similar to yours. I have converted some chaos warriors that count as grave guard. I have dyrads converted for use with my ghouls. I have empire, lizardmen, brettonian, and elven undead in my army. One of my vampire hero/lords is a bretonian lord on a Pegasus. I have some HE cav to use as blood knights or skelton knights.
Or you could do skulls, grave stones and bats.... oh wait... .... ok maybe skaven or ork vampires would be kool.
I went with elves for my VC where needed. A few elven characters, some dark elf models mixed with the old skeleton kit for warriors etc. I didn't take the theme all the way though, still have a bunch of normal undead as well.
I'm thinking a Twlight theme. Sparkly skined vampires and hordes of young girls as vampire fallowers rather than zombies. =D Oh wait. You said a cool theme. Oh well. Still not a bad idea.
dooing a vampire coast army would be cool, still keeping it with a human theem, but probs using a lot ofnorse and some amazon models- converting them up into an amazon pirate theme almost like a conquestodor army, or pirates of the carrebian?
I would forfeit my game if some painted their Vampire Lord with Glitter Paint. Think I would be unable to play because I would ROTFLMAO.
I really want to do a Nagash themed VC army. Taking a dash of inspiration from WoW, I imagine an army from cripple peak having many mutant ghouls, the lowly dregs mining the mountain for warpstone, which Nagash's necromancers use to fuel infernal machines that create powerful golems out of flesh and sinew. Like Abominations. I wonder how to represent Nagash himself, but since his power is waning at the moment you could probably use another character to represent the Shade of Nagash. Zombies glowing green with warpstone sickness, aboms = corpse carts? I dunno, I'm not familiar enough with VC to make a list, but the idea always intrigued me.