Daft Punk is an electronic music band based in Paris, France. Much of their music has been used at one point or another but four songs seem to have caught on with the YTMND audience.
"Harder, Better, Faster, Stronger"
"Technologic" was used in the fad featuring Osaka from the anime Azumanga Diaoh. The song was also used for some of the early iPod sites. Other sites will play around with the lyrics of the song, all related to technological actions (e.g., plug it, play it, burn it, zip it).
"Robot Rock" never really evolved as a fad compared to "Technologic" and "Harder, Better, Faster, Stronger", but the song itself became a popular music choice among sites depicting robots and robotic movement.
Max has stated on Ventrilo that he has received a Cease & Desist order from Virgin Records regarding use of Daft Punk samples on YTMND, though the continued existence of Daft Punk sites suggests he is either still in legal communication with Virgin Records or simply has no intention of complying.