Software Applications
Here are the best of breed - my favorite cross-platform, open source applications.
I use OpenOffice.org software for word processing, spreadsheet, presentation, and drawings. I use Scribus for Desktop Publishing.
I use Mozilla Firefox for browsing and Mozilla Thunderbird for e-mail.
A nice, full featured graphical text editor with syntax highlighting and many other bells and whistles is Vim, or Vi IMproved - a programmers text editor. I also use SciTe which is based on Scintilla.
I like a full featured graphics and photograph editing tool called the GIMP - the GNU Image Manipulation Program. I use Inkscape for creating and editing scalable vector graphics.
If you like to play or edit sound, Audacity is a good, simple audio editor suitable for recording, mixing, and editing ordinary tracks of CD-quality audio. VLC is a free cross-platform media player that supports a large number of multimedia formats without the need for additional codecs.
Games I enjoy playing are Tux Racer, BZFlag, Chromium BSU, Nethack, Never Ball, and Critical Mass. There are lots of games, such as Tux Paint, written using the Simple DirectMedia Layer, an open source, cross-platform multimedia library designed to provide fast access to the graphics framebuffer and audio device.
An open source, cross-platform native UI framework is wxWidgets (formerly called wxWindows).
There are some applications that are useful on Win32 where an equivalent application is already included in any major Linux distribution. I use FileZilla for FTP client and FTP server. I use PuTTY for an SSH client. I use WinSCP for a secure shell file manager. I use TortoiseSVN and TortoiseCVS for source code control. PDF Creator is a tool for creating PDF documents just by printing them from any Windows application.