I make no secret of the fact that I love ebooks, to be honest most of the time I am using an ereader - I have a HP Touchpad and an Iphone. I use the Stanza and Kindle app's and I think both are great. However neither of them are able to use all formats of ebook; for instance Kindle doesn't read epub files, which is annoying because most of the books I can get are in this format.
If you are finding this a pain too then I really recommend using Calibre, a piece of software that you download to your computer that converts files into the format you need them in.
Here you can see that I was able to get hold of a copy of One Hundred Years of Solitude by the marvelous Gabriel Garcia Marquez, but it was in Epub format (top left).
All I needed to to was select which format I wanted it in, in this case I was putting it on my Kindle so I went for Mobi (top right), and hit o.k and TA - DA! All ready to transfer using my iTunes!
This isn't an advert so I am not going to go into it any further than I have, but you can download it HERE if you so wish!