Physics and Astronomy

Max Planck Institute for Astronomy, Heidelberg, Germany
arXiv.org e-Print archive
Centre de Données astronomiques de Strasbourg
Resources in Astronomy
Planetary Fact Sheets
The Extrasolar Planets Encyclopædia
Exoplanet Data Explorer and Exoplanet Orbit Database
Astronomy Picture of the Day

Data Analysis

International Society for Bayesian Analysis
Data analysis: a Bayesian tutorial by D.S. Sivia with J. Skilling on Google Books
Bayesian Logical Data Analysis for the Physical Sciences: A Comparative Approach with Mathematica Support by P.C. Gregory on Google Books
Markov chain Monte Carlo in practice by W.R. Gilks, S. Richardson and D.J. Spiegelhalter (eds.) on Google Books

Computing

Algebra and Plotting

Maxima – a Computer Algebra System
gnuplot tips (not so Frequently Asked Questions)
matplotlib: python plotting

Numerics

Numerical recipes by W.H. Press et al.

Languages

Fortran
gfortran – the GNU Fortran compiler, part of GCC (including object-oriented Fortran 2003/8 features)
Fortran 90 Tutorial
Python
The Python Tutorial
Richard Gruet's Python page (including a quick reference for Python)

Documentation

Doxygen – a documentation system for various programming languages

Function Optimization

PIKAIA – a general-purpose function optimization FORTRAN routine based on a genetic algorithm

Various

GNU GDB Debugger Command Cheat Sheet
The GNU profiler
Open Multi-Processing

Dictionaries

dict.cc – “aims to be a platform for sharing linguistic knowledge”
LEO – includes a forum as well

Web Publishing

Content Management Systems

Drupal – an open-source CMS written in PHP

Web Design

NodeThirtyThree Design – the author of this and many other designs

Various

The Open Directory Project