I DMed a fun one a while back where the party was ambushed by displacer beasts. After winning the encounter, the party tracked the pawprints back to their lair, where they killed the rest of the pack. When they started looking around for treasure, they noticed some large bearskins, some clubs, and other hill giant-sized goods. It dawned on them that the pack of displacer beasts were pets of hill giants.
The hill giants, of course, had just come home while the party was fighting the displacer beasts, and were waiting outside the cave, clubs raised, to attack the party when they left.
This was at around sixth-seventh level or so, IIRC.