The Book Seer is a web application for recommending books. It takes the last book you read, and searches a number of other sites – Amazon, LibraryThing and BookArmy – to offer a suggested list of books to read next. It does this using those services’ publicly-available APIs.
Bookseer proved immediately popular, being picked up across the web, notably on the Guardian Books blog.
Peter Collingridge from Apt Studio has written more about this at The Long Tailed Book Seer.
The Book Seer offers people a short list of books from a range of sources in an informal way.