Leona Lewis won the third season of The X Factor back in 2006 – she went to No 1 with her single, "A Moment Like This", and again with "Bleeding Love". She's released five whole albums since leaving the show, ~and~ she recently joined Taylor Swift onstage during the 1989 World Tour. Leona is definitely still a winner.
After coming second in the sixth season of The X Factor, Olly Murs has released four albums, been nominated for five BRIT Awards, and supported One Direction on the US dates of their 2012 tour. He's also host of the most recent season of The X Factor.
Despite only coming fourth in the 2010 season of The X Factor, Cher Lloyd achieved success with her first single, "Swagger Jagger", which debuted at No 1 in the UK charts. Most recently, she's collaborated with Demi Lovato on her single "Really Don't Care".
Little Mix are probably one of the most successful groups to come out of The X Factor (they're also the only group ever to win the show) – they've just released their third album, and their most recent single, "Black Magic", went straight to No 1 in the UK. Fun fact: They also co-wrote Britney Spears' most recent single, "Pretty Girls".
After winning the 2008 series of The X Factor, Alexandra Burke's winner's single, "Hallelujah", became the top-selling single in the UK that year. She went on to release two studio albums, and most recently replaced Beverley Knight in the West End production of The Bodyguard.
Amelia Lily came third in her season of The X Factor in 2011, after being eliminated early and then reinstated after Frankie Cocozza was kicked off the show. Since then she's released a couple of singles, but her most recent career move has been towards theatre – she recently finished a run as Whatsername in Green Day's American Idiot: The Musical.
After coming fourth on The X Factor in 2008, Diana Vickers released several singles and took to the West End stage as the title character in The Rise and Fall of Little Voice. She hasn't done much music-wise for a while, but she's still acting, and made her way round the London Fashion Week circuit this season.
Joe McElderry was the resident northern cutie of The X Factor's sixth season, and he went straight to No 1 with his winner's single, a cover of Miley Cyrus' "The Climb". He's released four albums since then, and has appeared on a couple more reality TV shows – he won both Popstar to Operastar in 2011, and The Jump in 2011.
Matt Cardle won the seventh season of The X Factor in 2010 (yep, someone ~actually~ beat One Direction), and went straight to No 1 with his winner's single, "When We Collide". Since then, he's released three studio albums, and is currently playing a lead role in the West End's Memphis: The Musical, opposite Beverley Knight.
After coming second in the seventh season of The X Factor (yep, another person ~actually~ beat One Direction), Rebecca Ferguson co-wrote and released her debut album. Since then, she's released two more albums, and in 2012 she opened her own clothing boutique in London.
Shayne Ward won the second season of The X Factor, and we all remember his winner's single, "That's My Goal". He took a three-year break from music, but returned in 2010 with his third album, "Obsession". He's also appeared on Dancing with the Stars, and currently has a recurring role in Coronation Street.
Ray Quinn came second to Leona Lewis in The X Factor's third series, and signed a record contract with Sony, but he was dropped from the label in late 2007. After that, he went on to win the fourth season of Dancing on Ice. Fun fact: He also had a recurring role on Brookside before he auditioned for The X Factor.
Katie Waissel finished seventh in the seventh season of The X Factor, but her audition and controversial performances in the live shows were more than memorable. She's currently in a band, Red Velvet.
Stacey Solomon came third on the sixth season of The X Factor. Although she hasn't done much music-wise since, she did appear on the tenth season of I'm A Celebrity... Get Me Out Of Here!, and was crowned Queen of the Jungle. She also played a seagull in The SpongeBob Movie: Sponge Out of Water. ¯\_(ツ)_/¯
Jedward came sixth in The X Factor's sixth season, and have since released three studio albums – two of which went double-platinum in Ireland – and represented their country in the Eurovision Song Contest in 2011. They also regularly make appearances on TV, and starred as themselves in Sharknado 3: Oh Hell No! So, basically, they're probably the most successful X Factor contestants ~ever~.
OK. Maybe Jedward aren't ~the~ most successful contestants ever. After coming third in the 2010 season of The X Factor, One Direction shot to international fame, and are one of the best-known bands in the world. After releasing their fourth album, they became the first band ever to have their first four albums debut at No 1, and according to Forbes, as a group they're the second-highest-earning celebrities under 30. They've also stopped wearing matching outfits. And Harry probably hasn't cut his hair since their X Factor days.