Here are some random links that I find (or have found) useful at some point:
Tools | Graphics | News | Podcasts
Astronomy
Astronomy Picture of the Day (UK Mirror)
Each day a different astronomical picture with an explanation by a professional astronomer.
Hubble Space Telescope
For optical astronomers, this is one of the best instruments that we have. Although it is only quite small, as it is above the atmosphere, it 'sees' alot better than the current ground based telescopes. It has produced thousands of amazing quality pictures, most of which are available.
NASA ADS (UK Mirror)
Want to find an astronomical journal article? Use the NASA Abstract Data Service to get hold of abstracts to just about anything.
SOHO
SOHO is the ESA/NASA spacecraft that observes the sun.
Stellarium
Stellarium is a 'photo realistic sky generator' very much along the lines of Starry Night. However the advantage is that it is open source and free so it is possible to add changes to it. It is now up to release 0.10.1 (5 Feb 2009)
Useful for me
Terrain Generation
(3/10/2004) After all this time using my own cloud generation method, I discovered that Paul Bourke at Swinburne has already created landscapes with frequency properties although using a different method to me. He also has a page on planet simulation technique (although it suffers from mirroring). He also talks about 1/f noise. If only I discovered this site before I did it all myself.
Development
Cygwin
Provides a linux-like environment for Microsoft Windows.
GCC
GCC is the GNU Compiler Collection - use it to compile everything from C, C++, Fortran and even Java.
MinGW
Minimalist GNU for Windows. A collection of freely available and freely distributable Windows specific header files and import libraries combined with GNU toolsets that allow one to produce native Windows programs that do not rely on any 3rd-party C runtime DLLs. It is easy to download and install.
PGPlot
A set of routines written in Fortran that are used to plot scientific data. There are C wrappers that allow you to call the functions from C/C++ programs. There are ported versions for Windows but at the moment I haven't been able to compile a C++ program using PGPlot under Windows yet.
OpenGL
Paul Groves (ex UMIST?) has a good page about opengl (although his solar system model doesn't take into account the tilt of each planet's axis). I might consider using GLFW if GLUT doesn't work. As far as I can tell these are both ways to interface to OpenGL without the need to use OS dependent calls. OpenGL Win32 Tutorial. GLUT tutorial.
FFTW
The Fastest Fourier Transform in the West is way better than four1 from Numerical Recipes as it can even do more than one dimension and arbitrary input size. It is also cross-platform and free. I downloaded the Windows version, unzipped it, put the .lib file in my MinGW libs directory and the .h file in the include directory. It worked straight away!
Tools
Mozilla Firefox
The Browser, Reloaded. Previously called Mozilla Firebird and before that Phoenix. This browser is based on the Mozilla browser which sprang from Netscape. Confused? The only thing you need to know is that it is one of the best browsers out there that can be run on Linux, Windows and Mac. If you are like me and have lots of web pages open at the same time then tabbed browsing is far better than having lots of windows open.
PuTTY
PuTTY is a free implementation of Telnet and SSH for Win32 and Unix platforms, along with an xterm terminal emulator. It is written and maintained primarily by Simon Tatham.
VNC
VNC software makes it possible to view and fully-interact with one computer from any other computer or mobile device anywhere on the Internet. VNC software is cross-platform, allowing remote control between different types of computer.
WinSCP
WinSCP is an open source SFTP (SSH File Transfer Protocol) and SCP (Secure CoPy) client for Windows using SSH (Secure SHell).
Graphics
The GIMP
If you need to create graphics (everyone does at some point) then use the GNU image manipulation program. You can even use it on Windows!
Paint Shop Pro
Not a free product but I now own a proper copy after rather a long time using the shareware version.
Inkscape
My new favourite vector graphics program. It generates nice small and valid ps and eps too!
News & Views
Astronomy Blog
A place of random astronomy related ramblings in a weblog form. It covers everything from cosmology to the solar system to radio telescopes.
BBC News
A good source of news especially the science and technology section stories by David Whitehouse.
Astronomy Podcasts
The Jodcast
I'm involved with this astronomy podcast created by astronomers at Jodrell Bank.
For more astronomy podcasts check out the links on The Jodcast site.
Science/Maths Podcasts
Dr Karl
A science phone in from Australia's Triple J.
The Naked Scientists
Chris Smith and friends produce an hour long science show.
MathGrad
A great podcast about maths. Try it!