The National Oceanic and Atmospheric Administration has long had a number of centers and disparate web sites over which various forms of climate and climate-related data were available, including the National Climatic Data Center, the Climate Prediction Center, Climate Diagnostics Center, and various components of many other labs and research centers, not to mention climate info related to hurricanes and severe weather at the Tropical Prediction Center and Storm Prediction Center, respectively.
While it will take some time to pull together a truly comprehensive portal to make all of this data available in a more focused, user-friendly manner, NOAA has recently announced and made available an initial prototype of such a site, and it is already a fairly polished product with lots of information on climate, from links to observed and archived data to predictive systems to articles describing research results and goals, and much more. As seen on the first attached image, the main section of the page is divided into tabs covering a "ClimateWatch Magazine," "Data & Services," "Understanding Climate" and "Education," each of which leads to a number of additional tabbed subcategories.
One small but pretty cool additional feature is a scalable series of graphs toward the bottom of the page in each section of the site, called the "Climate Dashboard," that includes two tabs, one of which is a group of graphs with global variables related to large scale climate and how they have varied over time. These graphs can be set to start and end at any year from 1880 to the present. A second tab focuses on some regional climate and weather-influencing patterns and oscillations, such as El Nino and the North Atlantic Oscillation, and how they have varied since 1950. Clicking on any of the graphs within either tab will take you to a page with more details about the variable in question.
A red "prototype" link near the top of the main page provides more background on the portal project, along with links to many of the individual centers and data sources that comprise NOAA's climate functions.