Geostationary Operational Environmental Satellites (GOES): The orbital satellite keeping an eye on tropical depressions, hurricanes, and other weather related activity that may impact the U.S. : "Thanks to NASA technology and satellite data coupled with data from a National Oceanic and Atmospheric Administration (NOAA) operated satellite, you can see the tracks of storms from Arthur to Paloma from birth to death."
GOES-O: The latest in satellite weather study. It was launched earlier this year and was in testing mode when it shot some video and took pictures of Hurricane Bill as it headed toward the Bahamas on Aug. 20th.
Geotail: "The GEOTAIL mission is a collaborative project undertaken by the Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), and the National Aeronautics and Space Administration (NASA)." The original mission of this satellite goes back to 1992, where it studied and reported on the Earth's magnetotail dynamics (the planet's magnetic field as it is stretched 'behind' us by interaction with the solar wind). Currently (and since 1995) it has been continuing to collect information from a differing orbit on the solar winds interaction with the magentosphere.
Gravity Probe B: This mission is designed to test two of Einstein's thus-far unverified theories regarding is theory of relativity. I'll let the site tell you exactly what data they've collected and are going through (since 2005!) - "One is the geodetic effect, the amount by which the Earth warps the local space time in which it resides. The other, called frame-dragging, is the amount by which the rotating Earth drags local space time around with it." Not to kvetch, but how long does it take to tell whether he was right or wrong??
GRACE: 'The Gravity Recovery and Climate Experiment' were two satellites working in concert to make 'detailed measurements of Earth's gravity field to learn more about gravity and Earth's natural systems'. GRACE has been in orbit of Earth since 2002 and their big announcement is the scary amount of water that has 'disappeared' from India's underground aquafirs in the last 6 years.
Herschel Observatory: Herschel is a joint project which is being ran by the ESA to study proto star development in infrared vision. As their site puts it: 'Herschel can see the very dim infrared glow of cold dust that is only slightly warmer than the coldest temperature theoretically attainable. Herschel's view reveals that this star-forming region is even richer in cold and turbulent material than previously believed.'
HETE-2: 'The HETE program is an international collaboration led by the Center for Space Research at the Massachussetts Institute of Technology. Our collaborating institutions include the Institute for Chemistry and Physics (RIKEN), the Los Alamos National Laboratory (LANL), the Centre d'Etude Spatiale des Rayonnements (CESR), the University of Chicago, the University of California, Berkeley, the University of California, Santa Cruz, the Centre Nationale d'Etudes Spatiales (CNES), the Ecole Nationale Superieure de l'Aeronautique et de l'Espace (Sup'Aero), the Consiglio Nazionale delle Ricerche (CNR), the Instituto Nacional de Pesquisas Espaciais (INPE), and the Tata Institute of Fundamental Research (TIFR).' The primary mission of the satellite was to locate gamma-ray bursts. GRB's are extremely powerful events. This mission is listed under current, but there have been no updates in two years and at that time they were reporting that the satellite's batteries (after over 6 years of operation) were beginning to degrade substantially. It's possible that this satellite is no longer downloading valuable information.
Hinode: 'A collaboration between the space agencies of Japan, the United States, United Kingdom and Europe, Hinode's mission is to investigate the interaction between the sun's magnetic field and its corona.' Hinode was instrumental is studying the eclipse that occurred July 22nd, but it has also been studying sunspot and solar flare activity.
Hubble: Ah, my favorite mission ever. For anyone that's been living in a cave, locked away from any information whatsoever about the world, Hubble is the orbital telescope that has brought us images of deep, deep space. It studies our system's planets, gaseous nebula, star formation, black holes, quasars, even other galaxies... it is the greatest and I am so glad that they provided another service mission due to public outcry to upgrade and repair some of its systems so that it can continue to provide science, and let's face it - cool images, of objects that we'll never be able to see otherwise.