Of Monsters & Men Pack Billboard Aftershow Party in Chicago

Of Monsters and Men perform at the Billboard after party for Lollapalooza 2012 at the Double Door in Chicago, August 2012.See more: The Best of 2012: The Year in Music

The Jezabels and DJ French Horn Rebellion also appeared at our Lollapalooza-ending concert

The last notes of Lollapalooza 2012 rang out in Chicago's grant Park around 10 p.m., but the party was just getting started across town at club Double Door, where Of Monsters & Men and the Jezabels -- two of the hottest acts on Sunday's Lolla lineup -- hit the stage for a free aftershow concert hosted by Billboard and Starbucks Refreshers beverages.

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The line still wrapped around the block at 11 p.m. when Australian rockers the Jezabels started their set. The Sydney quintet -- led by sexy frontwoman Haley Mary -- treated the packed house to upbeat tunes from their award-winning 2011 debut album "Prisoner." Upbeat alt-rockers like "Endless Summer" and recent single "Rosebud" were received warmly by the crowd, and DJ French Horn Rebellion kept things grooving between sets. But it was obvious whose audience was in the house when Iceland's Of Monsters & Men took the stage just after midnight.

Watch Of Monsters & Men's Billboard Tastemakers Session

Lifting off with "Dirty Paws," the lead track from their acclaimed 2012 debut album "My Head Is An Animal," the six-piece indie folk band immediately showed why they're one the year's most buzzed-about new groups. Highlighted by the vocal interplay between singers Nanna Bryndís Hilmarsdóttir and Ragnar "Raggi" Þórhallsson, Of Monsters & Men held the crowd in rapt attention with their perfect harmonies and whimsical guitar melodies.

Three songs into the set, the group played an impressive cover of the Cure's "Close to Me," though it was their self-penned singles -- like their breakthrough hit "Little Talks," the charming acoustic ballad "Love Love Love" and recent single "Mountain Sound" -- that kept fans singing, swaying and clapping along throughout the band's 75-minute set, which served as the perfect ending to the long and loud weekend.