Each spring, the Rock and Rock Hall of Fame honors artists who have helped shape the legacy of popular music — and frustrates fans whose favorites didn't make the cut. Musicians become eligible 25 years after their first album release, according to the official rules, provided they "have demonstrated unquestionable musical excellence." The subjectivity of this last line has fueled debate since the first class was named in 1986. The induction committee has evolved with time to embrace a wider spectrum of music, including hip-hop and heavy metal, but the abundance of truly talented musicians has led to a long Rock Hall waiting list. Let's take a look at some worthwhile artists who are still waiting for their call.