They're kind of a cultural phenomenon. They appear, seemingly out of nowhere, become ubiquitous and gradually disappear. The musicians that create them fading back to obscurity after their 15 minute timer goes off. With some bands it's due to a general mediocrity-- they had their moment of greatness then receded back to mediocrity and thus obscurity.
With other bands and musicians it's more a matter of acccesibility. They're accomplished musicians with a small but loyal cult following who put out that one song that's accessible not just to their small cult of loyal fans but to a larger mass audience... They're never able to re-create that one magic moment that allowed them to connect with people beyond their small circle of fans. Some of them have no problem with this, others are distinctly bothered by the phenomenon and try their damndest to recreate that mass appeal that ever so briefly graced their otherwise obscure musical career.
Some of my favorite one-hit wonders include:
10. Pilot - Magic
9. Moving Pictures - What About Me
8. Joey Scarbury - Believe It Or Not (theme from The Greatest American Hero)
7. . The Refreshments - Banditos
6. A Flock of Seagulls - I Ran
5. Chase - Get It On!
4. The Outfield - Your Love
3. Escape Club - Wild Wild West
2. Player - Baby Come Back
1. Level 42 - Something About You
What are some of your favorites?