A few weeks back I posted a video that showed an Epub file being read on the Kindle. I just got an email and that Epub reader is now ready.It's called Booki.sh, and I love it. It works on your Kindle (it might not work on the K2 or K1), but it also works on just about every modern browser. It reads Epub and Zhook (a form of HTML5) files. BTW, this is the second browser based Epub reader from Inventive Labs, an Australian developer. The first was Monocle, and it was much simpler.
It's great. I like it because it's cross platform (apps are _so_ 2010). But I also like it becuase of the formatting options. Booki.sh has 3 line space options, 5 font sizes, justification, 3 font choices, and it has a night reading mode.
The fact it uses pagination is also a plus. You don't scroll to see more content; instead you turn the page. It's a must have feature, IMO; any app that lacks it is incomplete.