Music tends to have generational significance. Blues was a rebellious form of music years ago in the earlier part of this last century. Jazz likewise was a sharp break from standard popular music in the years after Blues first began its rebellious riffs. Rock became an outlet for youth in the 1960s and 1970s. Reggae, perhaps, picked up where Rock left off and carried us into the 1980s and then of course there was Hip-Hop.
What will children of the late 90's and early 00's take as their music? Perhaps Punk and Emo (short for Emotional or Emotional Rock) will speak to the next generation. I'm not talking about the Sex Pistols, but more modern Punk. This music has spoken to the angst, worry, and fear of teenagers for years, originating in England some 30 or so years ago. Punk and Emo music address pressing problems of group conformity and identity, relationships, love, rebellion, distrust of parents, concern about politics, and myriad other issues that are often the subject of every generation's rebel music. They aren't the same, but many see Emo as growing out of Punk.
Furthermore punk has impacted clothing and appearance choices not unlike previous rebel music. Gratuitous piercings and tattoos are often common, leather cloths, wallet chains, skull logos, and massive amounts of black or neon colored clothing are often characteristic of punk. Emo has likewise caused many youth to straighten their hair and die it black.
I'm no expert on Punk and Emo, although I did go to Warped Tour (2002 maybe) at what was then the Verizon Amphitheater in Virginia Beach, Virginia. Most true Punk and Emo supporters would likely bemoan all the "sell-outs" on stage there, but it was something different for me and let me at least begin to look into this community.
I'm also not sure that Punk or Emo has the same socio-historical importance of Hip-Hop, but perhaps that's my own bias. Who knows? Maybe Flogging Molly, Dashboard Confessional, Fall Out Boy, Good Charlotte are the new prophets among us.