What Defines a Great Recording Artist?

It's relatively easy to rattle off a list of great songs or albums, but what defines a great recording artist? Is it record sales? #1 songs? A showcase night on American Idol?

Producer Brian Eno once noted, The Velvet Underground never sold a lot of records, but everyone who bought one went on to form a band.

Ani DiFranco, on the other hand, sells a lot of records. But she does it on her own terms. DiFranco founded Righteous Babe, an independent label, long before the Internet was a series of tubes while reimagining an artists' business model--and redefining the role of the singer-songwriter--for the MySpace generation.

Bands such as the Grateful Dead and Phish reinvented their songs and set lists every night, creating a new concert experience for fiercely loyal fans and introducing a series of live albums and bootlegs that, arguably, are just as important as their studio work.

Jeff Buckley is fondly remembered for one amazing album. And, like a lot of artists who died too young, a catalog of posthumous releases (and an assembly line of vocal imitators) has tried to fill the void.

George Clinton receives royalties every time someone samples Parliament-Funkadelic. When does he ever get credit for the originals?

Leonard Cohen and Tom Waits are enjoying a renaissance in the twilight of their careers. They never experienced the mass adulation (and scorn) as when Bob Dylan plugged in an electric guitar, but where would popular music be without Various Positions or Rain Dogs?

Are younger songwriters like Jack White and Ryan Adams so prolific--with so many incarnations--that it's hard to identify a career-defining album?

How many of these artists qualify as the Greatest Artists of All Time?

That's up to you to decide.

Cast your vote for up to 15 artists by 5 p.m. Tuesday, May 19th, and tune in as we start the countdown of the 897 Greatest Artists of All Time later around Memorial Day.