Amazon and B&N often have lower prices on books as compared to Ibooks, and they have specials. The catch is that Apple won't let them sell books within the app, so you have to buy them in Safari.
I use the Kindle app and buy them from Amazon using Chrome. Auto d/l to my iPad. Amazon books are cheaper and have a better selection then the other guys.
Amazon and B&N often have lower prices on books as compared to Ibooks, and they have specials. The catch is that Apple won't let them sell books within the app, so you have to buy them in Safari.