Apple has just added the iBookstore to iTunes, a needed addition that should have been available since the introduction of iBooks, in my personal opinion. The iBookstore now allows users to purchase and download books from within iTunes and sync them with your iDevices rather than only making it possible to purchase the books on the actual iDevice.
Many notable book titles are currently discounted at $2.99 USD and several pre-order opportunities are also available. Users may also download samples of books and have them sent to their iDevices in order to allow them to preview the available titles before making a purchase.
Thanks to the recent implementation of Automatic Downloads, if you happen to have the service enabled, books purchased through the iTunes iBookstore will automatically be pushed to your iDevices, eliminating the syncing aspect altogether.