This may be more accurately phrased as how to survive using legally free software...

Browser: Mozilla Firefox

Newsgroup Reader: Mozilla Seamonkey

Vector Graphics: Inkscape

Image Converter: Squiggle, ImageMagick

LaTeX Editor: TeX Shop

Music: iTunes

DVD Ripper: HandBrake

Video Player: VLC

Generally Useful: Xcode, Image Capture (shift+command+4)

A quick note about a really cool tool that one of my labmates just told me about: Zotero.

It's a Firefox plug-in that allows you to save papers that you find on Google Scholar, Citeseer, etc., and attach notes to it, etc. Afterwards, you can go back to these saved papers and download the paper or the bibtex file. I can't believe I'd never heard of it before! Also available for download from the firefox plug-in site.