Google Groups - where people can answer questions
Sourceforge - where open source lives
Slashdot - relevant news
Krugle - A search engine for developers
Koders - Searching 225,816,744 lines of code.
Google Code Search - a new google beta
FEniCS: Finite Element Software developed by UofC, Chalmers, and Simula.
Sundance: Finite Element Software developed by Sandia
PETSc: Portable, Extensible Toolkit for Scientific Computation
Trilinos: parallel solver algorithms and libraries within an object-oriented software framework for the solution of large-scale, complex multi-physics engineering and scientific applications
www.linux.org: Linux's home site
tldp.org: The Linux Documentation Project - very helpful collect howto's and guides
www.linuxcommand.org: A site explaining how to use linux and why it is powerful.
www.debian.org: Debian's home site
aboutdebian.com: A good site about setting up Debian but not complete.
CTAN - the Comprehensive Tex Archive Network
Tobias Oetiker's (Not So) Short Introduction to LaTeX2e
The Comprehensive LaTeX Symbol List
Andrew Robert's Getting to grips with LaTeX
Keith Reckdahl's Using Imported Graphics in LaTeX2e
The Bibtex Bibliography Format
www.python.org: Python's home page
Enthought: Creators of SciPy, Chaco, Mayavi and other tools I use a lot.
Logilab: Another company that has quite a few general python tools.