Astronomy Links
Astronomy Picture of the Day: Great astronomy pictures with explanations, updated daily.
Sky-Map.org: An interactive map of the sky.
Stellarium: A great, free, open source planetarium program.
Physics Links
Large Hadron Collider Dashboard: Current information about the LHC Beam and experiments.
The Particle Data Group: Information about particle physics. A great resource for the latest measurements of physical constants and subatomic particles.
Weather Links
Penn State Weather e-Wall: An electronic version of the Penn State Electronic Weather Map and Meteorological Visualization Wall
General Computer goodness
ShareLaTeX: Online, LaTeX document creation and collaboration
Integration on a Casio or TI graphing calculator.