As you have discovered, there are a lot of websites out there now about covered bridges. These links are some of my favorite:

vermontbridges.com
An excellent site prepared by Joe Nelson devoted to covered bridges, with a lot more than just Vermont bridge info.

lostbridges.com
A good and growing source of information about covered bridges of the past.

nycoveredbridges.org
A good collection of information from the New York State Society for the Preservation of Covered Bridges

fhwa.dot.gov/bridge/covered.htm
The web site of FHWA aimed at the National Historic Covered Bridge Preservation Act

Other sites that you might enjoy

tfguild.org
Timber Framers Guild of North America, a nonprofit organization dedicated to promoting the benefits, beauty, and practicality of a timber frame structure.

bridgesite.com/funand.htm Fun and Learning about Bridges - an excellent source of all kinds of information about bridges.

And my favorite non-CB site - bridgecurmudgeon.com
A site devoted to education and discussion about controversial issues related to bridge engineering in general.