Melted Ghost Punch:
(Loved this as a kid)
red punch (hawaiian punch - do they still make that?) + 7-up stirred together in a big punch bowl with scoops of strawberry or orange sherbet floating on top. The sherbet melts and leaves a spooky melty look.
Orange juice mixed with creme soda is really tasty and looks appropriate for a Halloween party. (try it, it really is good!)
Here's a fun idea: get the tiniest gummies you can find like little spiders, or tiny-sized worms. Put one into each slot of an ice cube tray. Fill remaining space with water. Freeze. Pop these into drinks, preferrably something like sprite, that is clear.
Thoroughly wash some rubber gloves, and then fill with water till they're hand-sized. Freeze, and then float them in a punch bowl.
And, (of course it's not a drink, but what fun is a DC thread without someone going off topic
), a really easy, fun goodie bag for the kids: Get clear plastic (not rubber) gloves, and into each one, put one candy corn in the fingernail area. Fill the rest of the glove with popped popcorn. Tie at the wrist with a twist-tie. Add a plastic spider ring on the ring finger.