NASA's climate change site is at: http://climate.nasa.gov. It has excellent science content, graphics explaining key climate change science concepts, and beautiful images of Earth and Earth science data.

This post was edited by Juliette Rooney-Varga on Jul, 2013
Other great resources for accessible science information are:

NOAA's Climate site, http://www.climate.gov, is packed with up-to-date information and accessible data.

Climate Central: information targeted to a public audience with frequent references to the primary literature, updated frequently and linked to current events: http://www.climatecentral.org

Skeptical Science: critical analysis of misconceptions (and misinformation) that relies on primary scientific literature. See: http://www.skepticalscience.com

Climate Interactive: simulations and systems thinking around climate change and energy. You can find resources for the World Climate simulation role-playing game here. See: http://climateinteractive.org

You can search or browse resources that have been reviewed for both scientific accuracy and pedagogy in the CLEAN Collection (CLEAN stands for Climate Literacy and Energy Awareness Network). CLEAN resources are also searchable by resource type (e.g., activity, lab exercise, video, website, etc.), grade level, and content area.

See: http://cleanet.org/index.html