I'm using the following:
1) My previous eBook reader was the first gen Kobo so most of my purchases have been from them so I'm using Kobo ebook reader there, and its nice that it syncs my bookmarks with my Blackberry Bold and my PC.
2) I've Side-loaded Amzaon Kindle eReader on there using the process outlined on Good e-Reader's web site.
http://goodereader.com/apps/playbook...-android-apps/
3) For Library books I'm using the Overdrive Media Console
4) And finally any other books I'm using the Moon eReader which is also an Android app that was sideloaded. And I transfer the books over the Z drive when I plug it in.