Grand brothel (Big apple, chicken ranch, mustang ranch, etc). This small wonder, buildable with cerimonial burial, will make two unhappy citizens in its city happy, but growth will be slowed. It will take half again more ffod to increase city size. This reflects the disease and depravity associated withprostitution. Religeous societies can not build this this wonder, instead they can build the temple of purity and chastity. It has the same benefit and drawback - the followers of the sect don't breed.
On a more serious note, here's a idea about small wonders.
The first civ to build a small wonder should receive an advantage for being first.
Wall Street - The first civ to build wall street would also produce interest in the city in which it is built.
Battlefield Medicine - Any troop fortified for two turns in row is fully healed. Or maybe units heal at twice the normal rate.
Intelligence agency - Spy missions are some percentage cheaper. Or maybe first mission is free.
Heroic Epic - Better chance of producing leader.
Military Academy - Cost of builing an army is some percentage cheaper.
Pentagon - May build an extra army.
Iron Works - no bonus, its too rare.
Apollo program - One contenet citizen in city happy.
SDI Defence - Chance to intercept all missles, aircraft.
Forbidden Palace - Gain one free settler who requires no maintenance.