A couple of different answers:
1) The movie "That Thing You Do," was about a one-hit wonder band (The Wonders, or Oneders as the band's lyricist wishes it was spelled). The tune is very catchy, and totally believable as some 60's group's one-hit-wonder. I've always found it amazing that the songwriters for the film could create a song that was plausible as a one hit wonder. If you can do that at will, why can't you, you know, just go write an actual hit song? (For all I know the authors of the song have written other hits.)
2) Rock me, Amadeus, by Falco. Now, I guess in Germany-speaking realms, Falco is more than a one-hit-wonder, but the only of his songs that broke through to an English speaking audience was this one. The reason that it is, for me, the pinnacle of one-hit-wonders is that, in the song, there is a little narrative section, where he recounts a timeline of Mozart's life. He extends that narrative up to his composition of "Rock me, Amadeus," as though his composition were an important event in Mozart's life. That's a lot of moxy for a one-hit-wonder.