Check out ZuluReader, a new ebook reader app for Win Mobile and WinCE devices. It reads ePubs and RTF's. You can download it from my website www.zuluexpress.com
Don't judge ZuluReader on the website though lol. I am an app developer not a web developer, at the moment the website is pretty yuck but ZuluReader is way cool (IMHO).
I am looking for beta testers, so download it and see waht you reckon. As a bonus you get Steve Jordans' ebook The Onuissance Cells included in the install.