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COMEBACK: Robert Downey Jr.
In mid-2000, Downey seemed like he was headed for a career comeback when the Oscar-nominated actor — who had fielded multiple drug-related arrests since the mid-'90s — was cast as a love interest for Calista Flockhart on Ally McBeal. But after two more arrests, Downey was written off the show, sent to rehab, and placed on three-year probation. Vowing to get clean, over the next few years the actor rebounded personally and professionally, earning strong reviews for his roles in 2005's Kiss Kiss, Bang Bang and 2007's Zodiac. The actor officially reclaimed his matinee idol status in 2008, thanks to a little film called Iron Man, and an Oscar nomination for his role in Tropic Thunder.
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COMEBACK: Mickey Rourke
He began his movie career as a sex symbol. But that image quickly disappeared after Rourke picked up boxing in the 1990s. The fighting apparently took a toll on his handsome mug, and Rourke soon found himself stuck in a string of direct-to-video films. In 2005, however, Robert Rodriguez deemed him perfect for his gritty adaptation of Sin City, and in 2008 the actor picked up an Oscar nomination and a Golden Globe win for his role as a washed-up fighter in Darren Aronofsky's The Wrestler. Up next, a role as Whiplash in 2010's Iron Man 2. Can you say K.O.?
3 of 10
COMEBACK: Mariah Carey
The decade did not begin well for Miss Mimi. First came that whole Popsicle meltdown on Total Request Live, followed by 2001's box-office bomb Glitter. Within months, Virgin had paid the singer out of her contract. She attempted a comeback in 2002 with Charmbracelet, but didn't bounce back until 2005 with ''We Belong Together,'' the first single off her 10th studio album, The Emancipation of Mimi. She found hits with subsequent singles like ''Shake It Off,'' and continued her hot streak with 2008's E=MC2 — which sold 1.3 million copies — and 2009's Memoirs of an Imperfect Angel. (Its first single, ''Obsessed,'' was her highest debut on Billboard's Hot 100 since her 1998 hit, ''My All.'') On the film front, Carey is making Glitter a distant memory with a critically acclaimed performance in Precious.
4 of 10
COMEBACK: Ellen DeGeneres
DeGeneres found success in the mid-'90s when she came out on her sitcom, Ellen, but subsequent poor ratings led ABC to cancel the series in 1998. And though she tried her hand at sitcom success again in 2001 with CBS' The Ellen Show, the series only lasted one season. But the comedienne danced her way back into viewers' hearts in 2003 with her talk show, The Ellen DeGeneres Show, and a voice-over role in the hit Pixar film, Finding Nemo. Award shows love her as well — she picked up four Daytime Emmys for her talk show hosting duties, and hosted both the Primetime Emmy Awards in 2005 and the Academy Awards in 2007. DeGeneres recently celebrated her first anniversary with wife Portia de Rossi, and a new gig: permanent judge for American Idol.
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COMEBACK: Jackie Earle Haley
The child actor scored in 1976's The Bad News Bears — but puberty wasn't kind to him, and eventually the phone stopped ringing. Haley dropped off of Hollywood's map and began directing TV spots in Texas until 2006, when Sean Penn convinced Haley to return to the big screen for the first time in 13 years for the star-studded remake of All the King's Men. Soon after, Haley nabbed roles in films like 2006's Little Children (which earned him an Oscar nomination), 2009's Watchmen, and next year's Shutter Island. Up next: Haley co-stars in Fox's midseason drama Human Target, and will reinvent boogeyman Freddy Krueger in 2010's A Nightmare on Elm Street remake.
6 of 10
COLLAPSE: Lindsay Lohan
Lohan became Disney's darling of the decade after successful turns in 2003's Freaky Friday, and 2004's Confessions of a Teenage Drama Queen. But just as quickly as Lohan blossomed into a bonafide movie star, she wilted into one of Hollywood's most unstable actresses. After two DUI arrests in 2007 — not to mention two trips to rehab — the actress was stuck starring in Razzie-winning fare like 2007's I Know Who Killed Me. Though she's still finding work — albeit in low-profile fare like this year's direct-to-cable Labor Pains and a disastrous stint as ''artistic advisor'' for Emanuel Ungaro in October — you're more likely to see her on an episode of The Soup than in the multiplex. Perhaps Robert Rodriguez, director of Lohan's 2010 film, Machete, can turn things around for the starlet?
7 of 10
COLLAPSE: Mischa Barton
When The O.C. debuted on Fox in 2003, it became an instant hit and transformed the actress into TV's newest next big thing. But Barton would only stay in the O.C. for so long — the actress' character was killed off in 2006, and Barton has yet to find another successful project. Her latest endeavor, The CW's The Beautiful Life, was cancelled after only two episodes. As a result, she's currently better known for her behind-the-scene antics — including a 2007 DUI arrest (she pled no contest in 2008 and received three years probation) and a 2009 hospitalization — than her acting.
8 of 10
COLLAPSE: Joaquin Phoenix
The first half of the 2000's were good to Phoenix: He was nominated for an Oscar for Gladiator in 2000, gave solid performances in 2002's Signs and 2004's Hotel Rwanda, and earned another Oscar nod in 2005 for his role as Johnny Cash in Walk the Line. Then, Phoenix's hot streak suddenly cooled. In 2008, he declared he was retiring from acting to pursue a music career. Plenty suspected the actor was joking, particularly when he began appearing at events unkempt and unresponsive. But as soon as a video of Phoenix rapping — and falling off a stage — began circulating the web, people began to wonder whether the actor really had hit rock bottom. Of course, brother-in-law Casey Affleck is currently capturing Phoenix's so-called transformation on film for a documentary, so the joke could very well be on us.
9 of 10
COLLAPSE: James Frey
In 2003, addict-turned-author Frey published A Million Little Pieces, a memoir chronicling his struggle with drugs and alcohol. His big break came when Oprah selected Pieces for her book club in 2005. But things crumbled into a million little pieces in 2006, when The Smoking Gun published an article alleging that Frey had made up large chunks of his memoir. One infamous, uncomfortable appearance on Oprah later — he admitted that he lied in his book, much to the chagrin of the talk show queen — and the author went from wunderkind to laughingstock. (Random House decided to shell out cash to refund disgruntled readers.) One glimmer of hope came in May of 2008 when Frey released Bright Shiny Morning, which debuted at No. 9 on the New York Times' best-seller list despite mixed reviews.
10 of 10
COLLAPSE: Kanye West
The boisterous rapper's decade has been packed with big hits (''Jesus Walks,'' ''Gold Digger,'' ''Stronger'') and bizarre incidents (see: his infamous ''George Bush doesn't care about black people'' quote during NBC's live Hurricane Katrina fundraiser in 2005). But things officially fell apart for the rapper in September of 2009, when he interrupted Taylor Swift's acceptance speech for Best Female Video at MTV's Video Music Awards to declare that Beyoncé deserved the award instead. Though he quickly issued an apology and made an awkward appearance on The Jay Leno Show telling the comedian that he needed to ''take some time off,'' fans were hesitant to forgive. Soon, West's highly anticipated Fame Kills tour with Lady Gaga was cancelled. Even though he's currently lying low, we're guessing this is more of a time-out than a complete burn-out for West.