Free and open-source software

• Freshmeat (http://freshmeat.net/) lists and indexes lots of free and open-source software (as well as some commercial/proprietary projects). You can search by category, license type, maturity level, and various other features.
• SourceForge (http://sourceforge.net/) actually hosts open-source projects. They offer people who host their projects there web space, bug and version tracking, mailing lists, and so forth. Because SourceForge only lists projects that are actually hosted there, it has fewer projects than Freshmeat, but all the projects are licensed under some kind of open-source license.
• TheOpenCD (http://www.theopencd.org/) is a collection of open-source software that runs under Windows. Aimed at non-technical users, it's basically intended as a showcase to introduce people to open-source software.
• OpenOffice.org (also included on TheOpenCD) is a free (GPLed) office suite. It started out as StarOffice, a commercial project by Star Division in Germany, and was bought by Sun, which still sell a version branded StarOffice, but also released as much of the code as they could under the GPL. At the moment, the relationship between OpenOffice.org (GPLed and free) and StarOffice (cheap but not free, except on Sun's Solaris, and including some proprietary additions) is similar to that between Mozilla and Netscape — StarOffice is based on OpenOffice.org. I haven't used it myself, but by all accounts it's a perfectly reasonable office suite. It runs under Windows, Linux, and MacOS X.
• AbiWord (http://www.abisource.com/) is a free (GPLed) word processing program. I've used it, and it's been fine for everything I do. It runs under Windows as well as Linux (and a couple less common OSes). It will also run on MacOS X if you have an X server.
• GnuWin II (http://gnuwin.epfl.ch/) is another CD of free software for Windows.