The Internet Book Database Bookshelf and Book Information from ISBN Widgets.
Get Book information, Author, Title, Cover for millions of Books by ISBN using the Book Widget. No account required.
You can also insert the same book information directly into your posts by typing [ISBN:ISBNNUMBER] for example [ISBN:9780805079593]
You need an account at iBookDB to use the Bookshelf widget which shows random books from your bookshelf on your blog. Just enter your username, number of rows and number of columns and you are good to go. You can pick small or medium sized images.
To use the widgets go to Appearance->Widgets and drag and drop the widgets wherever you want. For an example on using and customization go to http://www.s1dd.com/2009/07/the-internet-book-database-book-information-widget/
Visit the Plugin Forum at http://www.ibookdb.net/forums/index.php/topic,2054.0.html