Essential Software for the average Joe

[speedwell68]

VLC, a quick and easy media player.
Kodi, for those that want a richer media experience.
Pinta, a simple graphics program.
Handbrake, for ripping DVDs or encoding videos.
Asunder, a great CD ripper.
Guake, an on demand terminal emulator, just press F12 and it's there.
Simple Scan, exactly what the name suggests.

[Linuxratty]

I have three different video players,just in case...I also use the Gimp with my Bamboo tablet, and Calibre for reading.

[Wadim_Korneev]

Type ‘restricted’ and the list of available software with that name will show up. Choose the “Ubuntu restricted extras” and click on the install button. This will install all the required multimedia tools you will need for that Scarlet Johansson movie or that Coldplay song.

[lysander6662]

Definitely f.lux for dimming the screen to the appropriate level at night. I do most of my work on the computer in the evenings and at night and once you start using it you cannot go back.

Of course there is Redshift, but I had mixed success with that, as I imagine other ATI users might. Here was the thread for getting f.lux to easily work

https://ubuntuforums.org/showthread.php?t=2352503

As for other vital installations, for me it's

Opera
Flash
Spotify
Pinta
f.lux
VLC
Steam

At the moment I use Rhythmbox for mp3 playback because I haven't found anything simpler. Amorok looks too bloated to me.