UltraMon is the one of the best application you should use if you are on multi monitor setup, it has all the most useful features and tool you would need to organise the display, screensaver, desktop wallpaper, windows, applications, desktop icons, display profiles, mirroring on multiple monitors connected to your computer.
Note: It can even support more than 10 monitors to provide custom display settings like different desktop resolution, separate or widescreen monitor wallpaper and separate taskbar for all these multiple monitors connected.
From the time I had setup the multiple desktop monitor this application is the most useful for me with extensive set of features like I can restore the desktop icons positions after connecting to extended monitor, toggle to set any monitor connected as primary, disable the secondary monitor with single click and lot more other things discussed below