I'm sure there are others but Amazon have the Kindle application available on the android market, you can download books direct to your phone and if you change your handset or want a proper ebook the books can be moved over.
Posted on my X10i using Tapatalk Pro and Swype Beta
you can create your own... thanks to GO DEV TEAM(GDT) you must convert any file to .txt though. i've learned one trick from pdf file to .txt is that on the pdf file click file then save as text than youre good to go.. http://goforandroid.com/ebook