Maps

Harvard Square Clickable Map
Hypertext Map of Harvard
City of Cambridge, Massachusetts GIS Map Library: General
MapBlast: This is by far the best mapping software on the web I've seen so far. It is used by the somewhat frightening LookupUSA service.
World and U.S. Maps: An early (but still quite good) clickable interface to maps. You can click here to get directly to 0hio.
U.S. Gazetteer: You can look up locations by name, and bring up zoomable adjustable images. More detail than the first, as far as roads and such. Or you can go directly to the map of the United States and zoom in from there.
USGS Home Page: The United States Geological Survey. They have lots of data. And several servers which seem at first glance to be redundant but not identical as you can see below. Maybe they are, as I have only glanced once.
USGS EROS Data Center: A collection of Map data files available on line.
USGS NSDI: The USGS node of the National Geospatial Data Clearinghouse, a component of the National Spatial Data Infrastructure. In other words, a lot of data that can be ordered, in tape format, and some stuff online.
USGS National Mapping Information: More of the same. They have a good description of some of their more interesting products.
GIS Online: Brandon Plewe wrote a book.