For me, it was perhaps simple-scan, a very simple and efficient GUI to scan documents. I used it with my Brother printer / scanner and it works like a charm. Especially since I do not scan stuff often, so a program with more complex UI would have the effect that I forget how to use it until the next time.
I was really surprised by some libre games with really good graphics for free software, like Xonotic or Unvainquished. And also very cool projects like Speed-Dreams, that is not as beautiful but is really promising
Otherwise, very cool stuff like Kdenlive, Ardour, LMMS, Puredata, … This is a long list! 😅