I have a few that aren't anywhere NEAR as "tech-geek-guru" centric.....:
Beesu - I dont evne know what it really IS.....but when I wanted to delete a folder and was gettingt an error message that it was unable to be deleted......moved....etc. I ran this and then it disappeared, I think it's some kind of "Menu Editor" for your Main menu selections that appear when you right-click, because the option to "Change Owner & Permissions" wasn't there UNTIL I ran it!

BleachBit - The best thing for my Fedora 17 machine since the Linux kernel! Everytime I run this app my machine emerges as if it's almost new. It gets rid of a lot of "fluff" that builds up over time.

GParted - The best tool for partitioning hard drives....both internal and network attached....hands down a necessity for any admin's Linux Tool Kit!

ClamAV - It may be hard to get it up & running, but once you do, it helps provide peace of mind just knowing that SOMETHING is minding the store and that no one can just waltz right in unannounced!