Open Library, "one web page for every book". The subject search is amazing: write one keyword, whatever, and the results are ordered by book's quantity. On the first places are the "subjects" that have the larger amount of books, specifying if it's a place, an organization... or just a subject!! You can browse the "shelves" for your book! And find a list of prolifics authors together with prominent publishers and a publishing history!!
They even link your book-description to WorldCat, so people may search for the nearest library so that they can borrow it!
Even more, they link the book to Amazon and others bookstores! And if you know the online version of the book, go and link to it!! Amazing!
Surfing on my memories, I never wanted to be a librarian. I only wanted to read books the whole day, and get paid for that...big mistake, librarians don't have time to read on duty hours!!
TinEye - a reverse image search engine. This will help me find those "red books" that patrons usually ask for! But be careful! This tool only searches images using images, so if you ar looking for a "blue book" use the cover image of a blue one!! You can use the Coverbrowser tool to give the url of the cover image!!
This is a different way of searching a book!