From Britney Spears delivering a pair of unexpected performances, to pop stars like Justin Bieber and Rihanna taking home trophies, to Beyoncé receiving the Billboard Millennium Award after a show-stopping number, the 2011 Billboard Music Awards were full of big surprises and unforgettable moments.

The brightest stars in music descended upon the MGM Grand Arena in Las Vegas on Sunday night (May 22) as the Billboard Music Awards -- broadcast on ABC and hosted by "The Hangover II" star Ken Jeong, returned to television with a bang. Ten years after rocking the BBMA stage with "I'm a Slave 4 U," Spears helped kick off the 2011 ceremony by joining Rihanna onstage for the remix of the latter's hit, "S&M." She later teamed up with Nicki Minaj for a reworking of her own single, "Till the World Ends," after Minaj played her latest pop-inflected hit, "Super Bass."

2011 Billboard Music Awards Main

Eminem, Rihanna, Bieber and Taylor Swift were among the big winners at the 2011 Billboard Music Awards, with Bieber and Eminem leading the pack with six awards each (the rapper's trophies, which included Top Artist, Top Male Artist, and Top Billboard 200 Album, were not given out during the telecast). Bieber took home the Billboard.com Fan Favorite Award as well as the Top New Artist Award; before taking the stage to accept the latter trophy, the teen sensation shared a kiss with his pop-star girlfriend, Selena Gomez.

Billboard Music Awards:

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Meanwhile, Rihanna was named Radio Artist of the Year and Female Artist of the Year, and Swift took home Billboard 200 Artist of the Year and Country Artist of the Year. "I used to watch the Billboard Music Awards and see my heroes like Shania Twain and Faith Hill win this," said Swift of the Country Artist award, before thanking her fans for helping her join that elite class.

The 2011 Billboard Music Awards celebrated musical legends as well as today's hottest acts, and Beyoncé fit snugly into both categories as she performed her kinetic new hit, "Run the World (Girls)," before accepting the Billboard Millennium Award. Beyoncé was honored by musical veterans like Barbra Streisand, Bono and Stevie Wonder, as well as First Lady Michelle Obama, in a video montage.

Justin Bieber, Taylor Swift, Eminem Top 2011 Billboard Music Awards

U2 also received a special salute by earning this year's Touring Award with their record-breaking 360 tour, and Neil Diamond capped off the night by taking home the Billboard Icon Award and performing his classic tracks "Sweet Caroline" and "America." "I don't know exactly what it means to be an icon, but I always wanted to be one," Diamond admitted.

The ceremony showcased a diverse mix of musical stars bringing their A-game to the stage: country acts like Lady Antebellum and Keith Urban, pop breakouts like Ke$ha and Taio Cruz, and rockers OneRepublic all dazzled the crowd at the MGM Grand. Cee Lo Green played "Lady Killer" highlights like "Bright Lights, Bigger City" and "Forget You" from a swirling, suspended piano, while Fergie let loose on a handful of high notes during the Black Eyed Peas' medley of hits.   

The 2011 Billboard Music Awards were also packed with unique onstage collaborations: R&B queen Mary J. Blige brought out hip-hop phenom Lil Wayne while performing her latest single, "Someone to Love Me (Naked)," while Pitbull joined forces with Ne-Yo and Nayer for his new hit, "Give Me Everything." Electro-pop upstarts Far*East Movement teamed up with OneRepublic's Ryan Tedder for "Rocketeer," and then invited Snoop Dogg onstage for "If I Was You (OMG)."

Photos: Billboard Music Awards Highlights

And tying the show together were the antics of host Ken Jeong, who first put his fingerprint on Las Vegas in his breakout supporting role in "The Hangover." After opening the show with a glitzy song-and-dance alongside Nicki Minaj and Train's Pat Monahan, Jeong discovered his inner Elvis with "Modern Family" star Eric Stonestreet, played banjo with Keith Urban, and quickly conceded to Blink-182's Travis Barker in a drum-off.

The 2011 Billboard Music Awards take a holistic look at artist performance based on key fan interactions with music, including sales data shared by Nielsen SoundScan, radio airplay monitored by Nielsen BDS, streaming data measured by Tubemogul and Nielsen BDS, social media consumption gauged by Next Big Sound and tour grosses tracked by Billboard Boxscore. Finalists and winners are determined by chart performance and social and streaming activity as chronicled in Billboard magazine and on Billboard.com during the eligibility period of Feb, 28, 2010 and Mar. 1, 2011.

Visit Billboard.com/BBMA for more info on the 2011 Billboard Music Awards, and tell us your favorite moments of the show in the comments section below. Thanks for watching!