Biology/Ecology

@WildEarth This is the Twitter stream for Wild Earth TV Wild Earth TV broadcasts from the Djuma Private Game Reserve. They have a web cam and also post live video from frequent drives through the reserve.

@UntamedScience This is the Twitter Stream from Untamed Science and the EcoGeeks Podcasts.

@EarthVitalSigns If you are looking for information about Global Climate Change from the Jet Propulsion Laboratory

Exploration/Adventures

@Rich_Wilson Rich Wilson is the Skipper aboard the Great American III which is participating in the Vendee Globe Solo-Non Stop around the world race. This Twitter stream includes frequent updates of his trip. Also check out sitesALIVE for teaching resources. Here are a few additional resources from Loraine a technology teacher at the Jackson School.
http://www.vendeelglobe.org/en
http://ehrweb01.aaas.org/sail/

Space Science

Space Shuttle Missions

@STS_119 STS 119 Discovery scheduled for launch on February 1, 2009.

@STS_126 This was the most recent mission from November of 2008. Check out this page for more information. http://www.space.gs/08/sts-126/

@NASA … for general information from NASA.

@Astrospace … space and astronautics news. http://www.space.gs/

Moon

@LCROSS_NASA… Lunar mission to the poles to see if there is water ice near one of the poles. See also http://lcross.arc.nasa.gov/

@LRO_NASA… The Lunar Reconnaissance Orbiter scheduled for launch in April of 2009. See also http://lunar.gsfc.nasa.gov/

Mars

@MarsScienceLab Here’s information on the next science mission to Mars due to launch in 2011.

@MarsPhoenix This was the twitter stream for Mars Phoenix which stopped transmitting from Mars on November 10, 2008. It is still active with news from Mars.

@MarsRovers Spirit and Opportunity’s official Twitter Feed. Its hard to believe that they have been on Mars for five years already. For more rover information check out: http://marsrovers.jpl.nasa.gov/home/index.html

Saturn

@CassiniSaturn From the Cassini Equinox Mission to Saturn

To Boldly Go…

@PlanetQuest Looking for planets beyond our Solar System with JPL.

It might be interesting to set up a iGoogle Page or a Pageflakes page with these feeds to use as part of a classroom science page. Or if students were studying a particular topic they have some resources to follow.
Feel free to add other similar sites in the comments.