Music that mattered—USA Today's anniversay look at milestones that changed music...

#1 - Napster (1999) "Shawn Fanning's file-sharing service, the first significant peer-to-peer music trading system, sparked a firestorm, prompting lawsuits from Metallica, Dr. Dre and major labels before a court order shut it down in 2001. Napster later rebranded as a pay service..."

#2 - Live Aid (1985) "The enormous benefit concert, staged largely inLondion and Philadelphia for 1.5 billion TV viewers, raised $245 million for famine relief in Ethiopia, canonized organizer Bob Geldorf and unleashed a glittery rock revue starring Paul McCartney, Queen, Madonna, U2 and scores more."

#3 - Michael Jackson on MTV (1983) "The R&B wunderkind broke the color barrier at the nascent music channel and blazed the trail for video innovation when Beat It, a nod to West Side Story, premiered in March. The epic zombie-themed Thriller followed in December."

#4 - N.W.A's Straight Outta Compton (1988) "Gangsta rap exploded in violent, explicit street stories, including the widely banned F--- Tha Police, fueling hip-ho's mainstream popularity and intensifying censorship debates and a culture war."

#5 - Smells Like Teen Spirit (1991) "Nirvana's punk anthem brought alternative rock to the fore and heralded the grunge movement's tsunami of Seattle bands from Soundgarden to Pearl Jam, rock's counteroffensive to big-hair metal. Kurt Cobain's 1994 suicide created a Gen X martyr."

#6 - iPods and iTunes (2001) "Technology allowed tailor-made playlists, and music became less of a communal experience as buyers cherry-picked vast online reservoirs and listened in isolation. Sales patterns reveal fewer superstars and a long tail of niche artists."

#7 - Radiohead (1997) "The most significant British group of the era risked 'commercial suicide,' according to its label, with the release of 1997's OK Computer, an experimental pastiche of ambient electronica, art-rock and post-punk that by 2005 was declared the No. 1 album of the past 20 years in Spin."

#8 - 'N Sync (2000) "While Backstreet Boys, Britney Spears and the Spice Girls enjoyed the spoils of the teen-pop trend, nobody scaled the charts like 'N Sync, whose bouncy No Strings Attached sold 2.4 million copies its first week, pop music's biggest opener ever."

#9 - Purple Rain (1984) "Already a star, Prince reached the stratosphere with the semi-autobiographical film and Oscar-winning soundtrack that yielded such indelible hits as 'When Doves Cry' and 'Let's Go Crazy.'"

#10 - SoundScan (1991) "The information system that tracks music sales altered the industry by revealing true data [via barcode scan at retail outlets] and replacing an inexact store-calling method tainted by errors and fraud."

Others of note:

#11 - Whitney Houston "The big-lunged R&B songbird became the first artist to score seven consecutive No. 1 hits, beating the record of six held by the Beatles and the Bee Gees. She paved the way for Mariah Carey's chart-topping vocal gymnastics and countless copycats."

#13 - The CD (1982) "The compact disc entered the marketplace, giving birth to music's digital revolution. It overtook vinyl in 1988 and cassettes in 1992."

#21 - American Idol (2002) "Churning out multiplatinum songbirds Kelly Clarkson and Carrie Underwood, the entertainment juggernaut is a rare water-cooler phenomenon in pop culture's hyper-diversified landscape."