UltraMon™ helps you manage multiple monitors. It makes it very easy to move an application to another window or across all windows (a must for applications with multiple pallets like Adobe® Photoshop®. Unfortunately UltraMon is not available for the Mac®.
Windows Desktop Search is a much better desktop search than the built in Windows XP search. It returns better results and has an easy to use interface. It's free.
FileBoss is a file management utility. Its great feature is it allows you to rename multiple files at once.
Wonder what's taking up so much space on your computer? The free WinDirStat gives you a visual map (treemap) of your hard drive, making it easier to clean it up.
CutePDF is free and allows you to create (but not edit) PDF files.
Audacity® is a free open source recording and editing software for Windows, Mac, and Linux/Unix.
OpenOffice.org is a free open source office suite for the PC (and Mac). It is a great alternative to Office 2007. It can read Microsoft Office formats.