Kelly Clarkson, the first Idol champion, holds the title of most albums sold by a show alumnus. The 27-year-old with the powerful voice has sold over 10 million records since 2003, generating a steady stream of cash. Clarkson's All I Ever Wanted, released in March, is currently at No. 17 on the Billboard 200.
Another popular career path for Idol contestants is taking their voices on to Broadway or on tour with roving productions of popular musicals. Clay Aiken, the quirky second-place finisher from the second season, boosted his 2008 earnings by performing on Broadway in the Monty Python musical "Spamalot."
Taylor Hicks, winner of the fifth season, is currently playing the role of Teen Angel in a national tour of Grease. Hicks has also toured extensively as a solo artist and released two solidly popular albums of bluesy tunes.
Constantine Maroulis, who finished sixth place in the fourth season, is the most decorated Idol-turned-Broadway star. This month, he received a Tony nomination for his leading role in "Rock of Ages."
Still, without a big-selling album, endorsement contract or solo tour, Maroulis fell just short of our list of top 10 Idol alums.
As Ms. Underwood can attest, a multi-platform approach is essential to post-Idol riches.