Southern Sudan, the world’s newest country, seems to me to be off to a bad start with its urban planning concepts:
I don’t think you necessarily want too much “planning” of a growing city at all. I’d like to see land used roughly as densely as market conditions warrant. But laying out street grids and such is necessary, and the goal should be to create a large number of relatively small streets—short blocks are good for walking, bicycling, etc. That kind of thing is especially important in poor countries; urban design that privileges the car is very bad for people who can’t afford one.