Using more than one monitor takes some getting used to, because it's typically not particularly intuitive. Under normal circumstances, Windows treats one of your displays as the "primary" display, and keeps all the key user interface elements--the Start button, task bar, and System Tray--inside that display. A second, or even third, monitor is like overflow space, where you can drag some application windows. Multiple monitor utilities like the $30 Actual Multiple Monitors (and its competitor, Realtime Soft's $40 UltraMon) make those "secondary" displays at least as functional as the primary display by adding those functions to the desktop(s) of the extra display(s).
Actual Multiple Monitors, like UltraMon, extends the Windows task bar to each active display, and shows only the windows and apps running within a particular display on that display's task bar; The program also duplicates the Start button and System Tray on each active display by default, though this can be disabled in the program's configuration dialog boxes. And like UltraMon, Actual Multiple Monitors adds an extra button to the title bar of windows or apps which snaps the window into another display--resizing the window, so it takes up proportionally the same percentage of display area as it did originally--instantly.
The program's attractive and comprehensive tabbed options menus let you quickly navigate to the particular aspect of the program you want to modify. Exclusions can be set up for specific programs, if you always want those programs to, for example, appear on a specific display when launched. And Actual Multiple Monitors (like UltraMon) can back up the position of any icons located on any display's desktop, so they aren't reshuffled or sorted anytime the display driver changes the desktop resolution. While AMM doesn't put a button on the title bar of windows to maximize those windows across all displays, an optional (off by default) right-click mouse command gives you that ability.
Like UltraMon, Actual Multiple Monitors will run on both 32- and 64-bit editions for all versions of Windows from XP through 7 (although AMM can run on either from a single download, whereas UltraMon has separate 32- and 64-bit versions). But unlike UltraMon, Actual's offering adds a Windows 7-style "Aero snap" feature to all windows by default, whether or not you're actually using Windows 7. That's cool, if you like that sort of thing.
At $10 less than UltraMon, Multiple Monitors offers virtually identical functionality, albeit with a hard, 30-day trial period. I liked the two button-action title bar mod; not so hot on the Aero snap. And let's be fair, the programs are so alike in so many ways, it's these little things that help distinguish them from one another. While Actual has its own keyboard shortcut menu, it can't do nearly as much as a straight up customizable command line, like UltraMon can hotkey for you. If that powerful feature isn't so important to you--and you crave visual appeal over performance (and don't have Windows 7)--Actual's product carries the day.