A very good place to start if you are interested in Ohio spatial data. The USGS is a major provider of data to private and public entities. Along with the Census Bureau Tiger files, the information they collect form the basis of most mapping in the United States. The Ohio EPA is another source of information and data. Yahoo and the Library of Congress are a good place to start.
Offerings change constantly as sites update their online collections.
Below is a sampling of library collections and links into the major mapping categories on Yahoo. One should re-visit often. Many of the maps seen on the internet are using their webserver software. This collects rain fall information and transmitts the data by radio link into a computer network. This is then available to the public within minutes of transmission.