10. ENTER GRUNGE: Sept. 29, 1991: Nirvana's "Smells Like Teen Spirit" video killed the hair-metal scene and signaled the ascendancy of grunge. The images themselves were an arresting accent, with the tattooed cheerleaders and what seemed like an underwater pep rally in a dank gymnasium. "The band, the sound and the imagery in the video was sort of a breath of fresh air — or a scream," said MTV series development guru Tony DiSanto.

11. CLAPTON UNPLUGGED: March 11, 1992. Only the most desperate of fading 1980s bands — Nuclear Valdez, Squeeze, the Alarm — responded to MTV's first requests to show off their acoustic chops. But fans responded to the intimacy and stars soon lined up: Bob Dylan, Led Zeppelin, Paul McCartney, Bruce Springsteen (who got nervous and insisted on an electric guitar) — and Eric Clapton, in his first performance since his son died after falling from a skyscraper window. "Everybody who was there felt something special was going on," says Van Toffler, president of MTV's music services. Clapton had to be talked into releasing the show on CD, and it became his biggest-selling album.

12. BOXERS OR BRIEFS?: April 19, 1994. Two years in office, President Clinton submitted to 90 minutes of questions on complex policy issues by 16-to-20-year-olds before a live MTV audience. Everything else was forgotten when 17-year-old Laetitia Thompson of Potomac, Md., asked: "Mr. President, the world's dying to know. Is it boxers or briefs?" "Usually briefs," the president replied, looking slightly nonplussed. Today, most presidential candidates use MTV to reach first-time voters.

13. HEH-HEH. COOL: March 24, 1994: Who'd have thunk that "Beavis & Butt-Head" would make the cover of Rolling Stone? When Toffler received a pilot tape of two adolescent cartoon characters playing baseball with a frog, he watched it nearly 100 times. "You have a feeling in your bones that there's something different about it that's unique and it will either flop miserably or succeed brilliantly." It was stupid, gross-out humor — but many older people secretly wished they could act that way.

14. REALITY BITES: June 23, 1994. It's hard to recall a time when setting up a group of strangers in a camera-filled home was a new idea. But the debut of "The Real World" "invented reality TV," says Thompson. "It's absolutely ground zero." And the inclusion of Pedro Zamora, who was gay and soon to die of AIDS, did more to promote tolerance than hundreds of public-service announcements. "It was probably the most riveting piece of television I had ever seen," says Brian Graden, then a young, gay man and now an MTV programming exec. "I had never seen someone like myself reflected back to me . . . it really changed things for a whole generation of gay people."

15. FEEDBACK LOOP: April 14, 1998: Jesse Camp wins the first "I Wanna Be a VJ" contest. Stuck in a rut, MTV was searching for some way to make its audience feel connected to the network. The wild-haired, willfully outrageous Camp seemed sent from central casting, and it was the audience doing the casting.