Of course there are. We cannot imagine new colours, for example.
The question is, are there things we don't even know we can't imagine?

I think we are in desperate need of a very, very good epistemological "theory of all". Or at least of a very good series of questions. We don't know what it means "to be", "to know", etc. Until we get a damn good definition/explanation of those things we're bound to not be able to wrap our heads around some questions.