Electronic programs for Linux
So you are interested in electronics, well so am I and here are a list of some useful electronic programs for Linux.
This list is by no means complete, it just contains the programs I would like to highlight.

Technically not a program but a collection of programs, but I like there effort so much that I'v given them a spot here.

A schematic capture program. (available as a Debian package)

You guessed it a PCB layout package. (available as a Debian package)

A spice3f5 circuit simulator, had been dead for some time, seems to have come back to life recently.
There web-page is way outdated though, there are no Debian packages, and it has an annoying license if you are going to use it commercially, it inherited it from the original spice3f5 license, you have been warned!
Here is a small part of the copyright notice:
Permission to use, copy, modify, and distribute this software and its
documentation for educational, research and non-profit purposes,
without fee, and without a written agreement is hereby granted,
provided that the above copyright notice, this paragraph and the
following three paragraphs appear in all copies.
If you are still interested in it here is how I compiled it.
Got the newest source, extracted it "tar -xzvf ng-spice-rework-15c.tar.gz"
./configure --enable-xspice --with-readline --prefix=/usr/share/gEDA/
make install (as root)

./configure will probably tell you that you are missing some libraries go get there -dev versions and you should be fine.
In case you are wondering how I selected the configure options have a look at http://www.brorson.com/gEDA/SPICE/x496.html
Actually the URL http://www.brorson.com/gEDA/ is also quite helpful.

Small Device C Compiler, a compiler for different micro-controllers among others PIC and 8051.

Haven't tried this one yet but it looks interesting. Draw a circuit and turn it into Verilog/VHDL code thingy.