I discovered katapult fairly recently myself.
Katapult + Amarok is really awesome. You can start typing in a word from the song title, press enter and it will start playing (complete with the album art showing). It's very convenient for quickly throwing on a track.
More neat stuff: This isn't totally KDE specific, but klineakconfig + lineakd + KDE plugins provides a really nice way to set up an internet/multimedia keyboard to use all those extra buttons at the top that would otherwise be useless. I've got a bunch of buttons controlling amarok, one that locks the computer, etc.