Click to listen to Britney Spears' "Till the World Ends"

Britney Spears is pop music's stealth avant-gardist. For years, critics have dismissed her as a cipher with a wisp of a voice. But from the minute she burst on the scene — heralded by the keyboard power chords of ". . . Baby One More Time" — her music has steered bubblegum into weirder, woollier territory. "Toxic" was a mélange of Bollywood and spy-movie guitar; "Piece of Me" was an essay on 21st-century tabloid infamy crooned over 22nd-century club rhythms. Then there's this year's "Hold It Against Me," which dissolves into a furious dubstep breakdown — easily the most assaultive beat on the Hot 100 right now.

Click to listen to Britney Spears' "Hold It Against Me"

Femme Fatale may be Britney's best album; certainly it's her strangest. Conceptually it's straightforward: a party record packed with sex and sadness. Max Martin and Dr. Luke, the world's two biggest hitmakers, are responsible for seven of 12 songs: big melodies and bigger Eurodisco thumps. But other producers go nuts, tossing the kitchen sink at Britney. The Bloodshy-helmed "How I Roll" is sputtering, oddly beautiful techno. In "Big Fat Bass," Will.i.am turns Britney into a cyborg obsessed with low-end. ("The bass is getting bigger!" she exults.) On nearly every track, Britney's voice is twisted, shredded, processed, roboticized. Maybe this is because she doesn't have much of a voice; it's certainly because she, more than almost any other pop diva, is simply game. Femme fatale? Not so much. But say this for Britney: She's an adventuress.

Britney Spears: A Life in Photos

“Tonight's the Night”

The lead cut and title track from this girl group's debut album, "Tonight's the Night" was written by 19-year-old bandmember Shirley Owens, who sings lead, and producer Luther Dixon. The band from Passaic, New Jersey met in high school, first calling themselves the Pequellos. The song's frank thoughts about sexual and emotional surrender was racy for the time, but that didn't stop the Chiffons from cutting a similar version immediately after the original came out. "We were the first female group to write some of our own material," band member Beverly Lee recalls. "We did have some say-so in our writing."