http://www.bestsfbooks.com
I was inspired by this HN post from a few weeks ago:
http://news.ycombinator.com/item?id=2978027
BestSFBooks ranks science fiction/fantasy books according to how many awards they've won or been nominated for. I included all the big ones (Hugo, Nebula, etc.) and also more obscure awards that I like such as SF Site Editor's choice. Once I had all the awards in there it was easy to start creating a New Book list based on award winning authors.
I could tell the app was working as soon as I saw the two book lists on the home page. They're excellent!
The stack is virtually identical to the stuff I used to build PickHealthInsurance. BestSFBooks is built with Rails 3.1.1 (HAML, Sass, CoffeeScript). It's hosted on Heroku and MongoHQ. I used the Twitter Bootstrap CSS toolkit, which I continue to find hugely innovative and useful. As always, data acquisition and cleanup was the hardest part.
I've wanted to build something like this for quite a while. As my time becomes more valuable, I'm becoming less tolerant of bad books. For a laugh, check out the "prototype" that I created ten years ago - http://www.gurge.com/amd/top100
Please send feedback!