Well you got the gambling, and the sex has already been suggested, throw in some liquor and other drugs and you'll pretty much have all the vices covered.
But, if you wanted to go the moral route, you could get a disco ball, a dance floor, and a loud stereo setup for some dancing. There's always the classic party games, Trivial Pursuit/Pictionary/etc. You might be able to rent a hot tub. Or just tell everyone to bring their PCs and have a huge LAN party. Always have lots of chips & dip... The people will usually entertain themselves.