The only costumes you can easily find in non-slutty form are witches.
Seriously, I HATE the fact that costumes, even those marketed to girls and tweens, have skirts up to, well, you know where. And there is no need, ever, to have anyone dress up as "Sexy Candy Corn" (seen it).
Here's a great example. When you get a picture in your head of "Little Bo Peep", what do you think of? Something like this, right?
Here's the "child" version of that costume:
And then, the adult:
This makes me more mad than I can say, and usually inspires a rant each Halloween, so I will be quiet for now. I have a standard, full length, with sleeves witchy outfit I wear every year, just so I don't have to go and get all fired up about this while I contemplate the wall of short skirts and thigh highs.