The Panic app I really miss is Audion. The Winamp-alike app that very nearly got bought by Apple to be rebadged as a little music player called 'iTunes'...
I've got an old PPC G3 Pismo laptop, and when I fire it up I always run Audion to play some music while typing. Loved the skins, I kinda wish the "Delicious Generation" of Mac interfaces would make a comeback. I think this was the default Audion UI:
The Panic app I miss most is Unison. Well, miss in the sense of miss it getting updated. It's still available.
Years ago, Unison and a fat Giganews subscription were fantastic ways to discover music.