Gnarls Barkley's ubiquitous megahit "Crazy" is the 2006 song of the year. It's the first single to top sales charts based on downloads, and in addition to being Grammy-nominated, it's also a frequent entry on informed best-of-2006 lists. We hear it at the gym, at work and while in line at Safeway.

Luckily, "Crazy" is a damned good single. Gnarls Barkley's debut album, St. Elsewhere, is an oddball pairing of gospel-influenced rapper Cee-Lo and indie hip-hop producer Danger Mouse, yet the disc delivers a unique, forward-looking midpoint between retro soul and alt-rock. "Crazy" is the disc's commanding gem, at once catchy and unsettled, danceable and ruminative. The uniqueness of "Crazy" is incomplete in only one way: its title.

Even excluding songs that just contain the word in the title, like "Still Crazy After All These Years" by Paul Simon or "Crazy for You" by Madonna, there are still dozens of fine songs titled, quite simply, "Crazy." How does this newcomer Gnarls Barkley's hit rate with other songs titled "Crazy"? Does it have what it takes to be an all-time great "Crazy" song?

The path to greatness for a "Crazy" song runs through two standards: Patsy Cline's hit version of the Willie Nelson-penned ballad "Crazy," and Seal's MTV-era dance-rock hit "Crazy." Both classics have been covered repeatedly, often by notable artists, but more importantly, these top two "Crazy" songs reveal what makes a "Crazy" song genuinely worthwhile. It's not enough to use the word as a passing adjective or mere descriptive staple. A truly great "Crazy" song imagines and realizes a state of removal and transformation, be it negative, dreaded detachment from the familiar, or positive, desirable freedom from the mundane.

Leading the pack is the Cline/Nelson classic, with its time-tested credentials in the repertoires of country, pop, jazz and rock. The song's languid melodic beauty is only as powerful as its self-deprecating sense of futility. "Worry, why do I let myself worry? / Wondering what in the world did I do?" sings the suffering shunned lover, so distraught that craziness becomes a convenient excuse for self-hatred.

Seal, on the other hand, advocates moderate craziness as a redeeming mass social balm. "We're never gonna survive / Unless we get a little crazy," he gently implores over a future-pop pulse, subtly suggesting that "miracles will happen as we dream." He's convinced some sort of unconscious release will make for a collective revolution.

Gnarls Barkley's megahit contends with these two great "Crazy" songs because, like them, it references craziness not as a term but as an inevitable destination. But GB's "Crazy" ups the ante, accepting the duality of insanity's repulsiveness and allure as normal. "There was something so pleasant about that place," Cee-Lo muses, as if he knows both Cline/Nelson's isolation and Seal's optimism. He enrolls us in sweetness and fear, accusing both himself and the listener of the mystery, and the fact, of our shared displacement.

Hard-rock "Crazy" songs tend to either love or hate craziness. Aerosmith's big '90s power-ballad "Crazy" melodramatically denounces the term as something opposite the idyllic life the singer begs from his girl. The Georgia Satellites' shuffling blues-boogie "Crazy" cutely promises insanity in exchange for love, boasting bizarre commitments like "I'd ride bareback on a six-foot monkey." Aussie hair-band Kings of the Sun like dangerous irresponsibility in their scorching "Crazy," proclaiming that wanton action is salvation.

Similarly, rapper Snoop Dogg's new disc starts with a bouncy, laid-back "Crazy" that understands craziness as proactive, carefree fun. For Snoop, crazy is normal and stable, and his loose SoCal territory is a place of freedom where he and a greater community are positively, as the warmly insistent chorus goes, "always up to no good."

Among many marginal "Crazy" songs by acts like R.E.M. and Kenny Rogers, a notable low point is the recent rap track by Kevin Federline, the former Mr. Britney Spears. This duet with his ex really belongs in a survey of songs simply titled "Superfluous" or "Silly." Here's hoping that nobody has ubiquitous 2007 hits with those titles.

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