My daughter wanted a Harry Potter theme for her 9th birthday!  We had so much fun doing this...We sent out the H.P. invites from Party America.  When the party guests arrived, they found a sign on our front door saying, "Platform 9 3/4" (i think that's the number??? it's been awhile, so check the book to be sure!) with an arrow pointing ahead.  We have a small foyer with another door into the house.  I put kraft paper from a roll over that door from top to bottom, with two or three vertical cuts in it so the girls could walk through.  I drew on the craft paper to make it look like a brick wall.  When they came through there, they were directed to a small table, where they had to guess the number of Bertie Bott's jelly beans in a small glass jar. (The closest guesser got the jar as a prize at the end.) Also, every year I set out a Scrapbook Page for all the girls to sign their name and birthday wishes for the birthday girl.  The girls then gathered into our living room where I had pushed all the seating up against the walls. At one end of the living room sat an old trunk and a box(for elevating the hat) on top of that, both covered in white sheets. on top of these went the Sorting Hat, an old costume witch's hat.  I stuffed some crumpled newspaper in it to help shape it so it looked a little shlumpy. underneath the white sheets i'd concealed the receiver end of our baby monitor. beforehand, i'd made a list of all the girls names and their attributes and what house they'd be in for the party.  I gave the list to Grandpa, who hid upstairs in the baby's bedroom and read the list. now, he'd never actually seen the movie, but he did a great job!  i gave him pointers on the voice he should use, and the times to pause before calling the next girl's name.  It was so great!  he called each girl up to sit in a chair by the hat, and then listed her qualities and sorted her into a house. 9 year olds are old enought to know it's not real, but they still want the magic of it all!  then they all got their glasses on (bought at party america) and their lightning bolts tattooed on their foreheads.  some of the girls had worn their own capes; very fun!  they got into their groups/houses, and were off on a scavenger hunt. I'd set up all these clues, and at the end they found each of their own bags of gold coins along with instructions to come back to the living room. once they were all back, they were then given directions to "Diagon Alley" where they would purchase their wands.  By this time Grandpa, (quite the helper couldn't have done it without him!)had gone down into our laundry room where we'd set up a counter and also all the wands behind. Once again, i'd let him know what to do to be most "movie like" and he did it! He really took his time in trying to match up the girl with her wand. My husband had gone out into the woods and cut down all the wands, and whittled them into shape; they were so authentic and cool looking! the kids who knew the movie LOVED this part. meanwhile, upstairs in the dining room I was getting ready for the feast. i'd closed off our pocket doors so that no one could see in there. i'd decorated it with all black, purple and gold tablecloths, streamers, balloons, etc...her cake was in the middle of the table; a simple 3 layer chocolate cake with chocolate frosting, set on a crystal cake stand. it had a small black cauldron in the middle, with dry ice "smoke" coming out of it; it looked great!  i had the lights dimmed a bit and lots of candles around.  I'd been lucky enough that day to go into the dollar store where they were unpacking these great glass decanters (for brandy, i guess?).  i bought about 12 of them.  these were all set around the table filled with sprite and colored with food coloring to look like potions!  each girl also got pop rocks and pixie sticks to make their own potions in their own H.P. gold goblets, which i'd gotten online. they got to then take these home as party favors.  when they came in to sit down, i'd written their names on placecards with white crayon.  they had to pick a seat and then color over the names on the placecards with black crayons and see if they'd sat in the proper spot and if not, they had to move!  that was a fun activity!  so they had a blast making the potions, they really fizzled up and popped! then i served them pizza and veggies with dip and fresh fruit. then back into the living room for a "Potions and spells" class; we just made up silly spells. then we did gifts and cake. i always make sure to take a picture of my child with the gift giver as she opens the presents, and then i send them in the Thank You notes. goody bags were given at the end; i'd washed out all their cups and filled them.  they each got a small bag of Bertie Botts jelly beans, and a small bag of the Harry Potter bubble gum, I can't think of the name, that i'd purchased online!  along with their H.P. glasses and wands to take home, this was a great parting gift.   we used all the H.P. plates, napkins, etc...solid purple tablecloth.  we had the H.P. theme music playing the whole time in the background to really set the tone. as i said before, we had a lot of fun doing this one!!!