Poll - are there any good prequels?

[jack]

This came up in the pub last night with the scifi society -- are there any good prequels, preferably scifi/fantasy? We thought of:

Children's books where the prequal is written second out of a series: Magician's Nephew, Charmed Life.
Series written out of order, such as Hornblower, Small Gods in TP.
Retrospective prequels: Asimov's robot stories became prequels to his foundation novels, though weren't at the time.

I decided that it's because prequels generally get written when an author (or their heirs) runs out of ideas, even more so than sequels, but if that's not the case they're by no means inherantly bad.

Can you think of any others?

Comments

[cartesiandaemon.livejournal.com]

I'm sorry, I take it back. I thought the case was fairly convincing (though hadn't considered it either way before last night) but this: http://www.ie.lspace.org/books/timeline/dw-timeline-smallgods.html seems a fairly considered opinion, and says there are some characters in common with the rest of the book. Oops.