I had the same problem - I've been trying Bluefire.

It's reasonably adaptable for settings (in some ways a little more than Stanza, and it will let you lock orientation), but won't let you change fonts (just sizes, but it's a decent serif font) or justification. (I do find it more generally readable than iBooks, though, and orientation lock is a must-have for me, since I often read in bed.)

It has lousy library sorting (you can sort by title and author, that's it, or search) but I'm okay working around that.