My son was born on Halloween, so we do costume-free (so the kids won't ruin them) Halloween themed birthday parties every year.
In the past we have booked parties at the pumpkin patch. We went to the one with a train and lots of different activities for the kids. The pumpkin patch lets each child choose a pumpkin as a take-home gift, and rides on the train came with the party package.
For a home party with games:
Wrap the Mummy - pair kids in two, give one a roll of toilet paper, and let them go. Makes great photos!
Halloween Charades - search google images for a vampire, frankenstein, a mad scientist, a black cat, a scarecrow, a werewolf (sp?), etc., print them, and cut them into small cards. Put them in a bowl and let each child choose from the bowl one at a time then act out his character while the other children guess.
Dr. I.B. Wicked, Mad Scientist Game - this is the classic "gross stuff" in a bucket game where the kids put their hand in a bucket covered with a towel or something so they can't see, and you put cooked cold spaghetti and other gross things in for them to squish and feel and figure out what part of Dr. I.B. Wicked's monster creation they are feeling. In this game I printed out a picture of frankenstein laying on a table and then drew lines pointing to each part of the body that would be in the bucket - spaghetti for guts, hard boiled and peeled eggs for eyeballs, baby carrots for toes, cooked whole cauliflower for brains, etc. I numbered each bucket 1-4, then gave everyone a pencil and as they felt in the bucket and identified what part it must be they wrote the number down on their sheets.
We also did "freeze" dancing to the song "monster mash" where you turn on the music, let the kids dance, then suddenly stop the music and everyone has to freeze, and whoever is in the best frozen moster pose gets a sticker or something.
For the menu:
If you "Julienne" slice hot dogs and steam them, they curl up and look exactly like worms. Serve these on hamburger buns with ketsup for bloody worm burgers.
this one took a little work but it was the hit of the buffet table... Monster Brains! Take a small, round, seedless watermelon, cut it in half, and CAREFULLY cut off (peel off) the rind with a paring knife. Just peel off enough to remove the green part of the rind, but leave the white part of the rind intact. Once all the green is removed, use your paring knife to cut and carve swirls into the white to expose the pink melon flesh between the areas you've left the white rind, and it looks just like a brain!!! Of course, birthday boy gets to be the first to cut into the brain at the buffet table.
We also made "Vampire Fangs". These were just peeled sliced apples (once peeled and sliced, dip them in a bowl of water and lemon juice so they don't brown). Serve them in a big pile on a serving platter with strawberry ice cream topping squirted over it for blood.
Last, we served "mummy toes". These were also a big hit. Little smokie saugages wrapped in a strip of flour tortilla and baked like pigs in a blanket. If you cut a toenail shaped nitch into the end of the teenie weenie before you wrap and bake it, that little nitch you've cut swells up with cooking and looks exactly like a toenail. Of course, these are served with more ketsup blood.
finally to drink I made Lime-aid (frozen lime punch). It is green and looked cool in the punch bowl with a piece of dry ice to make it smoke and with ice cubes I had made in advance with gummy worms frozen into them.
I got all of these ideas on familyfun.com. In addition, I tried to make these little "bone" biscuits they showed on their website, where you take pilsbury breadsticks can and cut the end of each breadstick to shape it like a femur bone, but when I did these they only ended up looking like doggie biscuits and so I didn't serve them at the party.
Oh... I almost forgot!!! For the adults I went to dollar store and got a skull shaped serving bowl, and mixed little tiny shrimp with red shrimp cocktail sauce and served this on a platter with crackers. Although it was delicious and who doesn't love chilled shrimp cocktail... using the little tiny shrimp and stirring them into the sauce directly made it really look like a pool of blood and maggots, and the adults got a real kick out of it!!!
Have a great time!!!