Since I have some very persuasive roommates, I'm probably going to be Kate Beckinsale in the advert below. Vampy, red, etc. However, in an ideal (non-college) world, I'd have a few other ideas. Read on, gals.
I have always wanted to be Nicole Kidman in Moulin Rouge for Halloween. I have reddish hair, and a serious love of corsets. It's a match made in heaven.
Denim & Diamonds Corsets, $234.99 at ebay.com, and $199.99 at ebay.com: I know it sounds like a lot of work, but all you really need are some stripper heels, some fierce makeup, a pair of boyshorts (or you could do opaque tights) and one of these corset/bustle combos. I know they're expensive, but one, they're so cute I could totally justify them, and two, wouldn't you want to wear these more than once? I'd totally be the girl wearing something like this to do laundry. No joke there. I just love this look because it's still sexy, but it's really original, well-thought out, and it just looks expensive (well, because it is). The peacock feather ensemble is a little darker and more sultry, whereas the pink and black number is a bit more sassy Parisian chic. AND JUST LOOK AT ALL THOSE FEATHERS. They would be so fun to flounce around int.
Joan Holloway from Mad Men: The slightly more PG costume I'd go for would be Joan Holloway from Mad Men. It's not super original, but it's very classy, and you could totally repurpose whatever dress you got for real life.
Learning Curve Dress, $248 at anthropologie.com, Zibo Midnight Shift, $258 at anthropologie.com: The key here is to get a wiggle dress (a fitted sheath) with sleeves that's about knee length, preferably in a wool or a jewel tone. Add a pendant necklace, a pair of sheer tights, and a retro pair of heels and you're good to go. This first option is a bit more vintage-girly, with the oversized bow on the bodice. Very sweet and refined and just overall adorable. The second option is a bit more Joan, a little more sultry and nighttime. I love the subtle pattern and slight variations in texture--it just makes the overall look feel so rich.
Images from justjared.com, allmoviephoto.com, ebay.com, ebay.com, swingfashionista.com, anthropologie.com, anthropologie.com.