Bowling Party:  Grab your friends and hit the bowling alley...This can be so much fun!  Call ahead to make sure that enough lanes will be available for the time that you would like to arrive.  Arrive before your guests to make sure to reserve enough lanes side by side and to set up the party.  Order appetizers, pizza, and soda.  When guests arrive, set up 'teams' and assign them a lane.  You don't really need to decorate, but if you would like to, you could bring helium balloons to tie on the chairs... (call the bowling alley to find out what they allow).  Bring party favors for your friends, such as, realistic rose temporary tattoos, cheap sunglasses, and Double Bubble bubble gum.  All of which can be found at Plum Party.  You could also bring a birthday cake decorated with bowling pin and ball candles.

Slumber Party:  Invite your friends over for a slumber party!  Make a big batch of popcorn with lots of butter, get the stack of movies ready!  More typical slumber party activities include makeovers, gossiping, pizza, scrapbooking, beading, and staying up late!   Decorate with this great slumber party themed partyware from Birthday in a Box. Click the photo for details.

Make your own personal pizzas... Ahead of time, make up the dough (make individual balls of dough -enough for one for each person).  Provide bowls of toppings, such as, pepperoni, chopped ham, chopped onion, chopped green and red pepper, sliced mushrooms, sliced tomatos, sliced black and green olives, etc... Also provide pizza sauce (the squeeze kind is the easiest!).  Allow each guest to prepare their own pizza.  Later, watch rented movies and pig out on junk food and cake! 
You could also have a Makeover Slumber Party...

Find many more themes at Shindigz.com, including Hello Kitty above, Batman Begins, Sweet 16, Denim and Bandanas, Football, Polka Dot Party, Tie Dye, Rock Star, Hollywood, Retro, Bowling, Shopping Spree, and many more!