I wouldnt call it "must have", but I came across a very handy app ... aFile Lite 1.2.0 by mAPPin Inc. Formerly known as Discover.
It allows you to transfer files to and from your phone using the WiFi in your phone. The only downfall thus far is having to restart the phone to use the files.
Does anyone know how to reload or mount/unmount the SD card without hooking it up to a PC? This program would be perfect if you could move the file over and it would show up right away.
aFile Lite v1.2.0 Application for Android | Productivity