Maybe it's that image of carefree bluebirds or just the lilting lullaby tone, but there's something about "Over the Rainbow" that warms the heart and makes cash registers ring.

The latest star turn for the tune written for Judy Garland's Dorothy in 1939's "The Wizard of Oz" came last week, when dreadlocked "American Idol" finalist Jason Castro plinked out Israel Kamakawiwo'ole's version of the song on the 'ukulele.

Castro's rendition not only kept him in the competition, it also spawned a 700 percent increase in sales and a huge jump — from No. 187 to No. 11 — on Nielsen SoundScan's digital songs chart for the 1993 version recorded by the late Bruddah Iz.

"The reason for (the song's) enduring success is simple: It's a great song with an inspirational message that can be applied to any situation," says Rolling Stone managing editor Will Dana. "I'd put it up there among the five most well-known songs in our culture."

Kamakawiwo'ole's sparse interpretation has starred in countless movies, TV shows and commercials, including a 1999 ad campaign for eToys.com and a 2002 episode of "ER." But the singer, who battled obesity, didn't live long enough to see his vision of Garland's classic resonate so completely with the masses. He died in 1997 at age 38.

Castro's decision to sing Bruddah Iz's version of "Rainbow" may have been as inevitable as it was deliberate, says Dana. Garland's version "came out a long time ago, and it's possible that (all) today's kids know is the Hawaiian interpretation."