I really hope they bring back the colony/outpost thing they had in Civ3. The best part of the Civ3 "single city challenge" games was trying to keep all those resource colonies hooked up by roads to your city. I had a number of scenarios I'd created in Civ3 that were based on the "single city" model that turned out to be completely undoable in Civ4 simply because there is no way to secure resources that are not within your city's cultural radius.