Overall, the greenest houses tend to be the smallest, most efficient ones because larger houses require more resource to build, maintain, heat, cool and light. That said, here are some links that may be helpful in making any house more efficient:
Smart Energy Living (Solutions for Colorado homeowners)
Rocky Mountain institute ( a Colorado non-profit focused on practical ways to improve energy efficiency; find information about appliances, lighting, water, building materials, household greenhouse gasses, indoor air quality , renewable energy and more).
Energy Star(find information about energy star appliances and general efficiency from his federal site).
E-Star Colorado (find a home energy rater, information about tax credits, and information about energy efficiency).