Dislodging Jack Johnson from the top after a three-week reign, Janet Jackson's Discipline bows at No. 1 on The Billboard 200. The Island Def Jam set moved 181,000 copies in the U.S., according to Nielsen SoundScan, becoming the artist's sixth chart-topper.

Her last two Virgin albums, 2004's Damita Jo and 2006's 20 Y.O., both debuted and peaked at No. 2, though Damita started with 381,000 while 20 Y.O. began with 296,000. Johnson's Sleep Through the Static (Brushfire) falls 1-3 with 92,000, a 12 percent sales decline.

4th World War, the first half of Erykah Badu's double album series New Amerykah, debuts at No. 2, selling 124,000 copies. It's the R&B singer's first studio effort since 2003's Worldwide Underground, an EP that began at No. 3 with 144,000. The second, as-yet-untitled portion of New Amerykah is due some time this summer via Universal Motown.

Rapper Webbie's Savage Life 2 (Asylum/Trill Entertainment) starts at No. 4 after selling 72,000. Sales were helped in part by the track "Independent," performed with Lil' Phat and Boosie, which is steadily rising on the Hot 100. Webbie's last solo effort, Savage Life, debuted at No. 8 in 2005 with 68,000.

Despite an 8 percent sales increase, Alicia Keys' As I Am (J) slips 2-5 with 57,000. Miley Cyrus' Disney double-disc Hannah Montana 2 (Soundtrack)/Meet Miley Cyrus experiences an 86 percent sales boost, propelling the effort 14-6 with 54,000. The young singer was recently featured on Barbara Walters' Oscar night interview special on ABC.

Speaking of Oscars, two Academy Award-winning titles are also featured in the top 10. With music from the Frames' Glen Hansard and Marketa Irglova, the Canvasback/Sony Music Soundtrax soundtrack to Once climbs 31-7 with 47,000 (+142 percent), after the duo won the best original song Oscar. The Rhino soundtrack to Juno falls 6-8 with 42,000, a 10 percent increase.

Sara Bareilles' Epic album Little Voice is down 7-9 with 37,000 (+1 percent), while Amy Winehouse's Universal Republic set Back to Black slips 3-10, also with 37,000 (-27 percent).

Debuting at No. 13, D4L member Shawty Lo's solo debut, Units in the City (Asylum), shifts 31,000. Dolly Parton's Backwoods Barbie starts at No. 17, the country legend's highest debut ever. Released through her own Dolly Records label, the new project shifted 27,000 units in its first week.

Other debuts this week include the original Broadway cast recording of Disney's The Little Mermaid at No. 26 with 20,000, the Afters' Never Going Back to OK (INO/Columbia) at No. 41 with 16,000, and Goldfrapp's Mute set Seventh Tree at No. 48 with 15,000.

Sales this week are down less than 1 percent from last week at 7.95 million units and down 6.4 percent from the same week last year.