Sam Worthington, 33
Following James Cameron's blockbuster Avatar, audiences chattered about the awesomely 3-D-rendered planet of Pandora, the white-knuckle action sequences...and a certain rugged ex-Marine. That would be Sam Worthington. ''I guess I have nowhere to go but downhill now that I've worked with James Cameron,'' jokes the Australian actor (who also costarred in 2009's Terminator Salvation as a deadly cyborg). ''I better hope he makes more movies, and that he liked me enough to keep hiring me, or it's over. I'm finished.'' Well, not quite. After playing Keira Knightley's husband in the drama Last Night, out in March, Worthington will star as the demigod Perseus in the big-budget remake of Clash of the Titans (out March 26).
Jaden Smith, 11
Since age 6, Will and Jada's son Jaden Smith has slowly been making his mark in Hollywood with supporting parts opposite Dad (as the precocious son in The Pursuit of Happyness) and Keanu Reeves (in 2008's The Day the Earth Stood Still). Now the 11-year-old will take on his first leading role in June's remake of The Karate Kid, as the eager student to Jackie Chan's teacher.
Mia Wasikowska, 20
Having caught our eye as a troubled gymnast on HBO's In Treatment, Mia Wasikowska has a busy 2010 ahead: The Australian actress will go from the set of a Gus Van Sant teen romance to shooting a big-screen adaptation of Jane Eyre. But first she'll fall down the rabbit hole as the star of Tim Burton's Alice in Wonderland (out March 5). As for slipping on the iconic headband, Wasikowska admits, ''There's a certain amount of pressure and anxiety when playing a character that is so well-known and so loved.''
Chloe Moretz, 12
Horror fans will remember Chloe Moretz from 2005's Amityville Horror remake, but she also has indie cred from her turn as the knowing little sis in (500) Days of Summer. Come April, she'll costar in the film adaptation of Diary of a Wimpy Kid, but it's really her role as foulmouthed mini-assassin Hit-Girl in the superhero flick Kick-Ass (also out in April) that has tongues wagging. Just a clip sent crowds at Comic-Con into a frenzy last year: ''I have this video on my phone from when I was walking on stage, and the crowd goes 'Ahhhh!' It's the best video ever,'' the 12-year-old laughs.
Alia Shawkat, 20
From costarring as a bassist in the Joan Jett biopic The Runaways, set for release March 19, to playing a Midwestern hooker opposite Ed Helms in the quirky comedy Cedar Rapids (not yet slated), Alia Shawkat, best known as the rebellious daughter from Arrested Development, will be growing up on the big screen this year. Her greatest passion, however, is for the HBO pilot she's developing with her Whip It costar Ellen Page. Called Stitch N' Bitch, the comedy ''makes fun of ourselves and hipsterdom,'' says Shawkat. ''Two girls move to L.A. and want to be artistic, but they have no talent.''
Reeve Carney, 26
Thank director Julie Taymor for putting Reeve Carney on the radar: He'll go from playing the Broadway superhero in Taymor's big-budget, long-gestating Spider-Man: Turn Off the Dark, set to unveil in February, to starring in her not-yet-slated movie adaptation of Shakespeare's The Tempest alongside Helen Mirren.
Grace Gummer, 23
You may have spotted Grace Gummer at a premiere on the arm of her mother (Meryl Streep), but the third of four Streep spawn didn't have a notable acting credit of her own...until now. In TeenNick's upcoming dramedy Gigantic, she'll be playing a starlet who's thrown back into high school. Of following in her mother's very famous footsteps, Gummer says: ''It just sort of happened, but it was something I was looking forward to doing.''
J. Cole, 24
The first rapper signed to Jay-Z's Roc Nation label (on the strength of his 2009 mixtape, The Warm-Up), J. Cole was featured on Hova's The Blueprint 3. Now he's readying his debut album, set to drop in late spring. ''The album is blowing the mixtape out of the water,'' he says. ''And the mixtape was great.''
Britt Robertson, 19
Where you've seen her: CBS' short-lived Swingtown. Next up: She'll star in The CW's midseason dramedy Life Unexpected (premiering Jan. 18).''It's a character-driven story, and my character is so complex that it was challenging. As a young actress, you don't get many opportunities to do that.''
Garrett Hedlund, 25
Where you've seen him: swinging swords with Brad Pitt in Troy. Next up: He'll star in December's Tron Legacy, the 3-D sequel to Disney's 1982 cult hit. ''The suit took two and a half hours to put on. But once someone clicked the activate button from a laptop 30 feet away, and you lit up like, breeee! it was worth it.''