maybe you could rent out like a club or somewhere to hang out....maybe rent a dj...
bon fires are really fun and if someone knows how to play the guitar that would be cool around the bon fire...
maybe a dancing competition...like you divide up into however many teams (if its around 20 divide into 3 teams or something) and you each get a half hour to make routines...but the team competing against you has to pick the song you have to make a dance routine to.
German Spotlight is fun when its dark out... one or two people have to go to a certain spot (a swingset is what i use) and they have each a flashlight and have to look around your yard (or wherever) to make sure no one hits the swingset (or wherever their spot is)...whoever touches the swing set (wherever ur spot is), wins...tell them to wear black if you play that