The biggest "mainstream" reader is the H2O and it's nice. If you want a bigger screen and better pdf support (via open android) you'll have to go Onyx or something similar.
This seems about to come out.
http://the-digital-reader.com/2014/10/30/onyx-boox-i86/
Again, Android.
Depends on your budget. There is no cheap large e-reader.