Penultimate is free now, I don't know if this is a promotion or a policy change.
It wasn't very expensive to start with, but I had never bought it because the screen shots in the app store looked ugly. However, in the last update it seems they have revamped it and now it looks rather elegant. I downloaded it last night and I like it, though it probably won't replace Noteshelf. I will try to post a more detailed review later.