taskbar — there's a separate taskbar on each monitor, and it displays only the windows that are on that monitor
alt-tab — using alt-tab only switches between the windows that are on that one monitor
wallpaper — each monitor can have different wallpaper

[$40] ultramon [wallpaper,taskbar]
[$15] display fusion [pro version] [wallpaper,taskbar]
[free] display fusion [free version] [wallpaper]
[free] VistaSwitcher [alt-tab]
[free] multimon [taskbar]
[free] zbar [taskbar,wallpaper]
[free] John's Background Switcher [wallpaper] — rotating wallpaper only, no fine static control