Someone in my social network recently tweeted about citethisforme.com so I checked it out.
The website is a free tool for rapidly constructing professional bibliographies for citations. Adding citations is very easy and accelerated with search – type in the book title (or ISBN), select the correct book from the search results, and the tool creates the citation details for you. The tool allows you to add a wide range of citation types:

You can have your bibliography formatted in a number of different styles:

Once your bibliography is ready, you can download it into word, copy / paste it, or export as BibTeX, Google Doc, or Evernote.

There are other features too, such as spelling and plagiarism checks. If you are working on something that requires professional or large bibliographies, it seems like a very useful tool.