Overdrive is another free one you can check out. It's somewhat similar to ibooks but without the big side margins. The library view isn't great but I only keep a few books on it at a time.
It does have a dictionary, but it always shows in white no matter if you selected the black, sepia or white background for the book itself.
Right now I mainly use ibooks and overdrive since they both show how many pages left in a chapter which is one of my favorite features.