This should have been my first mention for best free PC software, too. OpenOffice.org has offered free software for the PC and Mac for quite a while. It replaces the Microsoft Office suite and creates Adobe .pdf files with the click of a button. OpenOffice for the Mac is called NeoOffice.
StarOffice (a version of OpenOffice) is also offered through the Google Pack but is only offered for the PC.
I love the GIMP! It is by far my favorite software. It is a more advanced image program than I will ever need.
Fetch is a free (for educators) ftp program. It works perfectly.
Free video phone calls, too cool. Skype recognized my web cam automatically and was simple to set up.
Also for the PC, Google Sketchup is a free 3D modeling program.
Carbon Copy Cloner
Carbon Copy is a free backup utility. It makes a bootable backup of your Mac.