Here's the software selection I use for my daily business.
I just completed an installation of Ubuntu, which is a Linux distribution. I am not a very good user of Linux, I just know some basic functions. However, Ubuntu is a very good distribution, easy to use.
Here is a list of the programs I added to the standard version:
psutils + xpdf + pdftk + pdfjam + epstoedit
sun java + enscript + build-essential
tetex + kile + lyx + latex2html + hevea + texmacs + tex4ht
scribus + abiword
amsn + skype
xfig + transfig + qiv + gqview + imagemagick + ufraw
googleearth + qgis
inkscape + ipe + gnuplot + dia + povray + qcad + skencil
mplayer + codecs + audacious
octave + euler + yacas + koctave + axiom + wxmaxima + scilab + gnuplot + R + gnudatalanguage + freemat + extrema + pspp
ssh + vpnc
audacity + kino + wammu
windows fonts (msttcorefonts) + gsfonts-x11 + linux-libertine
Additionally, have a look at this blog, which proposes some steps to be performed right after installing Ubuntu: Linux on your desktop.
Of course, the package manager offers many more programs, but these packages are usually all I need for the every-day-use of my laptop.