Bike

Bicycle Colorado
Bicycle Aurora
BikeDenver
Denver Bicycle Touring Club
Better World club - Offers bicycle roadside assistance
The National Center for Bicycling and Walking
The League of American Bicyclists
Bicycling Life
Sheldon Brown - More bike information than you could possibly imagine
 
Transit

Regional Transportation District (RTD)
The Transit Alliance
Commuter Choice
Public Transportation
 
Carpool/Vanpool

DRCOG Ride Arrangers (metro Denver)
VanGo - Fort Collins
MetroRides - Colorado Springs
 
Walk

The National Center for Bicycling and Walking
Walkable Communities, Inc.
America Walks
Colorado Walks
 
Environment

Personal emissions calculator (EPA)
Greenhouse gas emissions calculators
Terra Pass
The Sierra Club
Grist Magazine
An Inconvenient Truth
 
Healthy Environments and Wellness

America on the Move
Livable Communities
Slow Food
Project for Public Spaces
Urban Land Institute
 
Articles

Article on Peak Oil and Healthcare
Peak Oil Medicine Website
Yes! Magazine's coverage of health care (various articles)
Another article on Peak Oil and Healthcare
Some thoughts on bicycling attire
Tips for happy bicycle riding
The best bike story ever
Think you can't bicycle because you have kids? Read this!