All your base are belong to us.2001 --- The opening scene from the "Zero Wing" video game (released in the Europe (but not the U.S.) in 1992) had dialogue which had been translated very poorly. It had been the topic of jokes on video game message boards and such, but had never become mainstream. Then in 2000, the Canadian band The Laziest Men on Mars made the song "Invasion of the Gabber Robots" using quotes from that game. And then, using this song, bad_CRC and associates made a flash music video starting with the opening scene of that game. This became the most popular parody of the "Zero Wing" game, and a big internet fad was born.
http://www.planettribes.com/allyourbase/video1.shtml(
note - a few short scenes with partial nudity and explicit words, er, I mean gestures)
Trogdor, the Burninator2003? --- A character used in an animation at the hometsarrunner.com website, created by Mike and Matt Chapman. Many people liked it, and "burninating" became a word people started using.
http://www.homestarrunner.com/sbemail58.htmlDragostea Din Tei AKA the Numa Numa song2004 --- Gary Brolsma posts a webcam recording of him enthusiastically lip-synching to the song "Dragostea Din Tei" by the Moldovan/Romanian music group O-Zone. It became much more popular and widespread than he ever expected (and in fact, he was not pleased with all the attention it brought him).
http://www.numanumadance.com/LEEEEEEEROOOOOOOY JEEEEEEENKINS!!!!!!!2005? --- A person who was playing the multi-player computer game "World of Warcraft" did something that ticked off the other players. The group of players playing the game were carefully planning out a strategy to defeat the powerful monsters in the room ahead. But Leeroy Jenkins shouts out his battle cry (his name) and rushes in without thinking. The other players quickly follow him in, still unprepared, and they get slaughtered. That part of the game was recorded and posted on the internet, where it became quite a hit.
http://www.ifilm.com/ifilmdetail/2671154?htv=12&htv=12(
note - strong language in this video (like I said, the other players were ticked))
Just a few here. Want to add to the list? Be my guest.