By now, I'm sure you've all heard that archeologists are claiming to have discovered the city of Atlantis in a mud flat located in Southern Spain, but there are plenty more "lost" civilizations out there just begging for discovery. While most of these societies did not lose their entire culture due to a massive tsunami that wiped them off the face of the earth, they instead disappeared for unknown reasons that have yet to be discovered.
Top Tenz has a fantastic article about the top ten civilizations that mysteriously disappeared and the stories are all fascinating. While you may recognize some of the group's names, like the Olmec (whose land was depopulated, most likely due to environmental changes or volcanic activity, although they may have been invaded) and the Mycenaeans (who may have been invaded, destroyed by class wars or destroyed by a natural disaster), many of the names of these cultures will be unfamiliar to all but the most dedicated history buffs.
The stories are not only fascinating in a historical context, but also a reminder that nothing lasts for ever. It's always interesting to reflect on the fact that no matter how much power an individual society wields during its peak, it is still prone to collapse -often so suddenly that the cause of the destruction is lost to history.