EOS EarthData

EOS-EarthData provides customized Earth Science data. They have over 700,000 data products that are easily searchable (see the 'Data Guides' under the Data tab for help and instructions). They have recently added a number of climate change data products and resources.
Go to http://eos-webster.sr.unh.edu and use the 'Data' tab to explore the EOS-EarthData data holdings.

Soil Climate Analysis Network (SCAN)

SCAN is a nationwide soil moisture and climate information system operated by the USDA NRCS. A standard SCAN site will collect precipitation, air temperature, soil temperature, soil moisture, snow depth, snow water equivalent, wind speed and direction, relative humidity, barometric pressure, and solar radiation.
Go to http://www.wcc.nrcs.usda.gov/scan and click on the map to access data for a specific SCAN site.

Hubbard Brook Ecosystem Study

Hubbard Brook is a long-term ecological research site in White Mountain National Forest of New Hampshire.  Research at Hubbard Brook has produced some of the longest continuous data bases on hydrology, biology, geology, and chemistry of the forest and its associated aquatic ecosystems.
Go to http://www.hubbardbrook.org and click 'Data' then 'Data Resources' to search the data holdings.

Data Enhanced Investigations for Climate Change Education (DICCE)

DICCE provides satellite data for oceanic, atmospheric, and terrestrial processes. Data is available globally and can be displayed in multiple formats or downloaded for further analysis.
Go to http://gdata1.sci.gsfc.nasa.gov/daac-bin/G3/gui.cgi?instance_id=DICCE-G_Basic

USGS Water Resources

The U.S. Geological Survey provides access to current, past, and future water data, maps, and publications. They also provide information on recent water projects and events around the country, as well as educational resources.
Go to http://water.usgs.gov and click the 'Data' tab to search their data holdings.

National Snow and Ice Data Center

NSIDC supports research on the Earth's frozen reamls: snow, ice, glaciers, and frozen ground.  They provide access to many cryosphere-related data sets, visualizations, and educational materials.
Go to http://nsidc.org/data/docs/daac/nsidc0271_ease_grid_swe_climatology/browse/viewer.html to view their visualization tools. Click on 'Home' or other tabs to access other data or classroom materials.

NH Dam Bureau

The NH Dam Bureau manages dams, lake levels, stream flows, and surface and groundwater in the state of New Hampshire. They also provide real-time data of many water and climate variables at dam locations throughout New Hampshire.
Go to http://www2.des.state.nh.us/RTi_Home and click the map to choose a dam location and view the real-time data.

Sea Ice Box

The Sea Ice Box is a part of the Ice Planet Earth project, which works to promote understanding of Earth's polar regions.  With this interface you can compare sea ice extent between different months and years.
Go to http://iceplanetearth.org/seaicebox/index.jsp and follow the links next to either the Arctic and Antarctic to view ice extent visualizations

Interactive Temp Tracker

An interactive map that draws on data from the National Climatic Data Center's database, displaying record night and daytime temperatures in the United States.
Go to http://www.climatecentral.org/blogs/climate-centrals-record-temperature-tracker/ to see the interactive map. Click "Play month" to animate an entire month.

ImageJ

ImageJ is a free image processing program that can display, edit, analyze, process, save, and print images. Use it to calculate area and pixel statistics, do geometric transformations, spatial and color calibration, etc.
Go to http://rsbweb.nih.gov/ij/index.html and follow the links to learn more about it, and download the program.