kvakvak, afaik right now there is only Books.app ( http://code.google.com/p/iphoneebooks/ ) for the iphone\touch that supports very limited formats and no landscape mode. Some people use a hack that makes use of Safari's ability to read pdf\doc\xls to read their materials, but I don't think it's worth bothering if you're just a casual (e)book reader. Better wait for proper 3rd party app in about 2 months time. (There's even gonna be MS Office for iphone? http://www.appleinsider.com/articles...hone_apps.html )

A good blog about ebook devices (including iphone, among the devices that he owns):
http://wowio.wordpress.com/