In Allison Pearson's new novel, I THINK I LOVE YOU, David Cassidy is the teen pop stud du jour. But there were many that came before and many more that came after. Here is a taste of some of the most crushworthy pop stars of the past 50 years. Sixteen tracks including music by Leif Garrett, Britney Spears, The Beatles and, of course, the dreamy Mr. Keith Partridge himself.