Do you guys remember these ladies? The spooky Wiccan all-girl goth band from Scooby Doo? This was the first costume I thought of, and it would be great to do with friends. I'm using their first appearance, in "Scooby-Doo and the Witch's Ghost" to make their costumes, though they have wardrobe changes depending on the episode.
Source: The Other Side
Thorn, the leading lady in red, might require some alteration to a red velvet tank dress to make her signature drop sleeves and sash, but cutting up a cheap red scarf should do the trick. Her gloves are easy enough to find, and ankle strap black shoes shouldn't be a problem. To get her hair, find a black wig with red sheen or red highlights, then top her makeup off with fangs and her black/red lipstick!
Luna, the red headed keyboard player, can be done with a little bit of ingenuity. While she appears to have the most tame outfit, a purple skirt suit shouldn't be that hard to find, the trick is in making her look cohesive with the rest of the ladies. Short purple gloves, knee high black boots, hoop earrings and her necklace should do the trick of portraying her character. Oh, and don't forget her purple/black lipstick and fangs!
For Dusk, the drummer and lovely lady in green, obtain a blond wig and tie it up in pig tails, then apply green and black lipstick with fangs. Her collar necklace should be easy enough to find (in your closet or otherwise) and her other necklace is easily made if you cannot find it. A green velvet dress with long sleeves will work, and green triangle earrings shouldn't be hard to make or find. Carry around drumsticks to make yourself easier to identify, but don't go smacking people with them!
PS: Bonus points if you memorize the songs!