Alt-Tab Thingy - Press alt & tab together to switch between open programs. Very useful. This program adds a graphical display with a screenshot of each open program. (XP)
Free Desktop Clock - Change the clock in the system tray to various formats. (XP)
Desktop Sidebar - Creates a sidebar similar to the one included in Vista. Very useful. (XP/Vista 32/64bit)
Dexpot – Create and manage virtual desktops (up to 20) enabling multiple workspaces for organizing the desktop environment, either by task, application type, by priority, or any other way you fancy. Each virtual desktop is independent from the others and can have individual wallpaper, resolution, and icons (or no icons at all). Easily switch between desktops from the tray icon, or via hotkey, or use an automatic desktop slideshow that rotates all virtual desktops. Lots of configuration options/features including; dynamically change icons to display active program on each desktop, pre-defined transparency levels for certain apps/windows, fully configurable hot keys and screen edges, move and copy windows from one desktop to another, set up rules to automatically move, copy or close windows and more. (XP/Vista 32/64bit)
Free Launch Bar - Neat replacement for the Windows Quick Launch bar. Adds quite a few useful features. (XP/Vista)
LogonStudio - Easily change the Windows logon screen. Hundreds of downloadable skins are available. A great way to customize your computer. (XP/Vista 32/64bit)
MagicFolder - This Vista sidebar gadget is great for those who download lots of files. The gadget lives in the Vista sidebar. Drag a file to Magic Folder and it automatically moves the folder based upon predefined rules, which you can edit. A real time saver. (Vista 32/64bit)
MouseShade - Highlights the area around the mouse pointer and dims the rest of the screen. This would be useful for reading long web pages, presentations, demos, and a variety of other purposes.
RK Launcher - Very neat tool that allows you to create a launch bar for programs and folders. You can even replace the Windows taskbar.
Greenfish Icon Editor - Use this program to change icons or create your own personalized icons. (XP/Vista 32/64bit)
Task Arrange - Lets you change the order that programs appear in the taskbar. It's a great program for those who generally have many programs running at once and like to have them appear on the taskbar in a specific order. I use this all the time. (XP)
Taskix - Have you ever wanted to put the icons in your taskbar in a different order? This program does it! (XP/Vista 32/64bit)
Xneat - Extends the functionality of Windows. Features include: Arrange taskbar items, show/hide windows, and change what appears of the taskbar. (XP/Vista 32bit)