What are some good birthday party ideas?

i like to plan ahaid and im turning 14 in a couple months, im having around 14 girls, and 2 guys. i live in chicago area. i have a trampoline and a swing set in my backyard, is there any places i could have it? i was thinking about renting a big water slide but there all like 700 dollars. i really need help! any themes , places to have a teen girl birthday party in joliet area, or places in chicago to rent a good but reasonably priced water slide?