Quickreader works for me. You can also consider converting it to .mobi (on your pc with calibre) and using the Kindle app.
Once you have an epub reader like quickreader on your ipad you can use "open with" in dropbox to open the file in the reader app. You obviously need the dropbox app for this.
Everything is app based and you pass files around between apps.
As long as that ePub is DRM-free, there are many e-reader apps that can read it, such as: iBooks, Bluefire Reader, Stanza, etc. There are many more available ... more than can be listed!
You can us the "Open In..." function in Dropbox to have the book open in the dreading app of your choice. As long as you have WiFi, you can just leave your books in Dropbox and open them when you will.