Flash mobs -- when a group of people appear in one location unexpectedly and usually put on some sort of rehearsed performance -- have practically become a staple of YouTube in recent years.

While one would expect it to quickly become a tired phenomenon, we've seen so many creative variations on it that viewers continue to seek them out. We've seen flash mobs with lightsabers. Flash mobs in the Ohio State University Student Union. Bollywood flash mobs. Planet Hollywood flash mobs. German ballet flash mobs.

According to our YouTube search data, big interest in the term "flash mob" started to rise in mid-2009 and remained steady until last December, when it hit a huge peak around the holiday season's most popular trend. Since we're still seeing new flash mobs appear each week, we thought we'd review which flash mobs were the most-viewed ever. These 10 run the gamut of style, size, and language, but they're all pretty entertaining:

(May take a moment to load. Watch the full playlist here.)