make a fashion show. gather everyone to a large area, set up a stage. then invite all parents to act as audience. get 3 volunteers from the parents to act as judges. rent a wardrobe for the day and ask everyone to come in normal clothes. then dress everyone up and make them walk between the audience (on a red carpet or stage)
Make sure you get funny items for your fashion show. for example get big wigs and lots of glitter. for the boys bring big hats and a tie. if you don't want to rent a wardrobe, make it a 60's or 70's theme and ask everyone to dress as crazy as possible. You can mix and match and switch the outfits. give out certificates for craziest hair and best make up.
For games you can always make a scavenger hunt and look for 70's items around the place, give them all 15 minutes, the one that comes back empty handed gets splashed with paint and glitter, and the rest get to keep the items they found. This may be expensive but if you make a small group this will be fun and enjoyable for kids and teenagers.
This may not seem very original but the only way to get original is to mash up to unoriginal things. if the birthday is in breast cancer awareness month. get everyone to wear pink and only pink, have pink balloons, serve pink lemonade, tell everyone to wrap their gifts in pink then hide a green object somewhere, now tell them this is only where its pink, this may seem lame but once there is one color everyone wants to find another. A simple dance party would a dress code will make the pictures look nice.
Dress codes themes and scavenger hunts are the biggest keys to a good party, if its someones birthday in summer i think its best to make a swimming party because everyone loves to swim and they don't even have to just relax by the pool (or beach), how about in the invitation u tell people to get certain swimming caps like for example say you have 30 people tell 15 to get red swimming caps and 15 to get blue so it will be easier to make teams, then simple water racing games or marco polo with some music in the background.