Map Resources
Adventure Cycling Association
This is a great organization, leading the way in the development of bicycle routes across the U.S. Their route maps, though expensive, are prized among tourists as the best and most complete in the country.
American Bike Trails   Maps of bike trails in all states for sale
Bikely   Maps of thousands of routes of all lengths and difficulties submitted by riders worldwide, many with detailed maps, elevations and descriptions
BikeMap   Maps of thousands of routes of all lengths and difficulties submitted by riders worldwide, many with detailed maps, elevations and descriptions
Delorme Atlas & Gazetteers  Available for every state, shows all county roads
Google Bike Maps  
Gives you point-to-point directions with bicycle-friendly routes. Does not distinguish between paved and unpaved bike trails, though.
Illinois DOT   Downloadable bicycle maps of all sections of the state
League of Michigan Bicyclists
Resources, open group rides in Michigan, maps for sale
Map My Ride  General biking site with news and comprehensive ride-mapping features
Michigan DOT   Downloadable bike maps and biking information
Michigan Trails   Comprehensive trail atlas of Michigan - book
The Natural Resource 
Interactive map to locate bike shops across ohio
Ohio Cross State Bicycle MapsPrinted maps of bike routes across Ohio (fee for maps)
Pedalling   Self-guided bicycle routes with maps and descriptions submitted by riders worldwide
Pedal Pushers Online   A general interest biking site with a "Map Your Ride" feature, allowing you to create a mapped road route from any point on the globe to any other point
Pennsylvania DOT   Maps of bike routes in Pennsylvania
Road Bike Routes   Mapping site and source for road routes
TMACOG   Map of bicycle trails in northwestern Ohio (PDF)
Trail Resources   Commercial on-line vendor of midwest bicycle touring books and maps
Wisconsin Bike Routes   County maps and detailed descriptions of state bike routes
Wisconsin DOT   Downloadable maps of all Wisconsin biking trails

Route & Trail Suggestions
American Discovery Trail   The first U.S. coast-to-coast non-motorized trail system
Bike Tour Archive   Index and descriptions of thousands of bike tours worldwide, submitted by riders who have taken them
Bikesafe Touring   Bike routes across the State of Pennsylvania

The Cowboy Trail   195 mile Nebraska hike/bike trail
Cycling Around Lake Erie   A guide and on-line resources for this international cycling trip (book available)
Cycling the Erie Canal   Guide, map and on-line resources (book available) on this 625 mile N.Y. trip
Cycling the Finger Lakes
On-Line resources (book available) for cycling this attractive tourist region
Erie Canal Heritage Trail   85 mile section of the Erie Canal from Lockport, NY to Palmyra, NY
Finger Lakes Routes   9 bicycle routes with maps and descriptions
GAP/C&O Trail   Dedicated 318 mile bike trail from McKeesport, PA to Washington D.C.
Grand Illinois Trail   535 mile loop trail in Illinois
Indiana Trails   Index of Indiana's multi-use trails
Jennifer's Trail List   Dozens of good trails/routes with descriptions, maps, elevations and other detailed information
Katy Trail   Map and details on this highly popular 264 mile Missouri bike trail along the Missouri River
Ohio DOT   Index, maps and descriptions of all Ohio Bikeways
Ohio & Erie Canal Towpath Trail
60 mile path south from Cleveland
Rails to Trails Conservancy   
Index and maps of all Rails to Trails bike paths in the U.S.
Rails to Trails TrailLink   Find a trail near you using an interactive map
Railtrails and Towpaths   List of Ohio trails and towpaths
Ride This Bike   List of worldwide biking trails with on-line resources
Route Verte   Regarded as the world's best bicycle touring venue, in Quebec Province
Trails from Rails   List of bike touring trails
Travel Wisconsin   Bike touring information & destinations
Trails   Subscription site resource for finding trails in the U.S.
Youghiogheny Trail   43 mile trail along the Youghiogheny River from McKeesport to Connellsville