http://www.mcny.org/exhibitions/current/The-Greatest-Grid.html
I guess I had always envisioned early Manhattan as a $24 piece of flat streetless land on which some enterprising Dutch people laid out the numbered streets like you do in SimCity.
Instead, the island was hilly and rocky, and by 1811 (start of a large-scale planning survey) was already home to a large variety of properties on parcels of different shapes and sizes. The transformation required a lot of earthmoving and peoplemoving.
There's an exhibit (through July 15, 2012) at the Museum of the City of New York, and a companion book.
Barcelona is currently (and has for years) changing to a grid-pattern of streets from a less-planned structure. You can see where it's been done on Aerial views.
Here's an interactive map from the NY Times comparing the original 1811 map to the modern-day grid:
http://www.nytimes.com/interactive/2011/03/21/nyregion/map-of-how-manhattan-grid-grew.html (http://www.nytimes.com/interactive/2011/03/21/nyregion/map-of-how-manhattan-grid-grew.html)