Ebook Central's Bookshelf function is a great way to keep track of ebooks without having to search for them repeatedly. Before you use the Bookshelf you must sign up for a free Ebook Central account.
To add a book to your bookshelf, click either the "Add to Bookshelf" link on book's Detail Page,
or the "Add to Bookshelf" icon on the Reader page.
To get to your Bookshelf, click on the Bookshelf link on the top toolbar on any Ebook Central page.
On your Bookshelf, books are listed in alphabetical order, but you can organize them further using the Folders function on the left side of the screen. The number of annotations you made in a book will be shown.